fix PR 111259 invalid zcmp mov predicate.

fix PR 111259 invalid zcmp mov predicate.

The code changes are from Palmer.

root cause:
In a gcc build with --enable-checking=yes, REGNO (op) checks
rtx code and expected code 'reg'. so a rtx with 'subreg' causes
an internal compiler error.

solution:
Restrict predicate to allow 'reg' only.

gcc/ChangeLog:

	* config/riscv/predicates.md: Restrict predicate
	to allow 'reg' only.
Reviewed-by: Palmer Dabbelt <palmer@rivosinc.com>
Acked-by: Palmer Dabbelt <palmer@rivosinc.com>