RISC-V: fix thinko in riscv_register_move_cost ()

This seeming benign mistake caused a massive SPEC2017 Cactu regression
(2.1 trillion insn to 2.5 trillion) wiping out all the gains from my
recent sched1 improvement. Thankfully the issue was trivial to fix even
if hard to isolate.

On BPI3:

Before bug
----------
|  Performance counter stats for './cactusBSSN_r_base-1':
|
|       4,557,471.02 msec task-clock:u                     #    1.000 CPUs utilized
|              1,245      context-switches:u               #    0.273 /sec
|                  1      cpu-migrations:u                 #    0.000 /sec
|            205,376      page-faults:u                    #   45.064 /sec
|  7,291,944,801,307      cycles:u                         #    1.600 GHz
|  2,134,835,735,951      instructions:u                   #    0.29  insn per cycle
|     10,799,296,738      branches:u                       #    2.370 M/sec
|         15,308,966      branch-misses:u                  #    0.14% of all branches
|
|     4557.710508078 seconds time elapsed

Bug
---
|  Performance counter stats for './cactusBSSN_r_base-2':
|
|       4,801,813.79 msec task-clock:u                     #    1.000 CPUs utilized
|              8,066      context-switches:u               #    1.680 /sec
|                  1      cpu-migrations:u                 #    0.000 /sec
|            203,836      page-faults:u                    #   42.450 /sec
|  7,682,826,638,790      cycles:u                         #    1.600 GHz
|  2,503,133,291,344      instructions:u                   #    0.33  insn per cycle
   ^^^^^^^^^^^^^^^^^
|     10,799,287,796      branches:u                       #    2.249 M/sec
|         16,641,200      branch-misses:u                  #    0.15% of all branches
|
|     4802.616638386 seconds time elapsed
|

Fix
---
|  Performance counter stats for './cactusBSSN_r_base-3':
|
|       4,556,170.75 msec task-clock:u                     #    1.000 CPUs utilized
|              1,739      context-switches:u               #    0.382 /sec
|                  0      cpu-migrations:u                 #    0.000 /sec
|            203,458      page-faults:u                    #   44.655 /sec
|  7,289,854,613,923      cycles:u                         #    1.600 GHz
|  2,134,854,070,916      instructions:u                   #    0.29  insn per cycle
|     10,799,296,807      branches:u                       #    2.370 M/sec
|         15,403,357      branch-misses:u                  #    0.14% of all branches
|
|     4556.445490123 seconds time elapsed

Fixes: 46888571 ("RISC-V: Add cr and cf constraint")
Signed-off-by: Vineet Gupta <vineetg@rivosinc.com>

gcc/ChangeLog:
	* config/riscv/riscv.cc (riscv_register_move_cost): Remove buggy
	check.