bpf: correct pseudo-C template for add3 and sub3

The pseudo-C output templates for these instructions were incorrectly
using operand 1 rather than operand 2 on the RHS, which led to some
very incorrect assembly generation with -masm=pseudoc.

gcc/

	* config/bpf/bpf.md (add<AM:mode>3): Use %w2 instead of %w1
	in pseudo-C dialect output template.
	(sub<AM:mode>3): Likewise.

gcc/testsuite/

	* gcc.target/bpf/alu-2.c: New test.
	* gcc.target/bpf/alu-pseudoc-2.c: Likewise.

gcc/config/bpf/bpf.md

@@ -131,7 +131,7 @@
         (plus:AM (match_operand:AM 1 "register_operand"   " 0,0")
                  (match_operand:AM 2 "reg_or_imm_operand" " r,I")))]
   "1"
-  "{add<msuffix>\t%0,%2|%w0 += %w1}"
+  "{add<msuffix>\t%0,%2|%w0 += %w2}"
   [(set_attr "type" "<mtype>")])
 
 ;;; Subtraction
@@ -144,7 +144,7 @@
         (minus:AM (match_operand:AM 1 "register_operand" " 0")
                   (match_operand:AM 2 "register_operand" " r")))]
   ""
-  "{sub<msuffix>\t%0,%2|%w0 -= %w1}"
+  "{sub<msuffix>\t%0,%2|%w0 -= %w2}"
   [(set_attr "type" "<mtype>")])
 
 ;;; Negation

gcc/testsuite/gcc.target/bpf/alu-2.c

+/* Check add and sub instructions.  */
+/* { dg-do compile } */
+/* { dg-options "" } */
+
+long foo (long x, long y)
+{
+  return y - x + 4;
+}
+
+/* { dg-final { scan-assembler-not {sub\t(%r.),\1\n} } } */
+/* { dg-final { scan-assembler {sub\t(\%r.),(\%r.)\n} } } */
+/* { dg-final { scan-assembler {add\t(\%r.),4\n} } } */

gcc/testsuite/gcc.target/bpf/alu-pseudoc-2.c

+/* Check add and sub instructions (pseudoc asm dialect).  */
+/* { dg-do compile } */
+/* { dg-options "-masm=pseudoc" } */
+
+long foo (long x, long y)
+{
+  return y - x + 4;
+}
+
+/* { dg-final { scan-assembler-not {\t(r.) -= \1\n} } } */
+/* { dg-final { scan-assembler {\t(r.) -= (r.)\n} } } */
+/* { dg-final { scan-assembler {\t(r.) \+= 4\n} } } */
+