Tighten regexps in gcc.target/riscv/_Float16-zhinx-1.c .

The original "mv" regexp would match
.ascii  "\254\254\375\002e2N6\013\231,\354NDmvVP0]\304\312F!biZ\025\211"
in the .gnu.lto_foo1.0.32528183c9deec41 section.

gcc/testsuite/
	* gcc.target/riscv/_Float16-zhinx-1.c: Tighten regexps.