[RISC-V][PR target/118241] Fix data prefetch predicate/constraint for RISC-V

Fix typo in comment spotted by Peter B.

	PR target/118241
gcc/
	* config/riscv/predicates.md: Fix comment typo in recent change.

(cherry picked from commit bf7162b321128ba93521a824e5a7a00d1cc3d1f8)