RISC-V: Fix rtl checking enabled failure with -msave-restore.

RISC-V: Fix rtl checking enabled failure with -msave-restore.

Found with an rtl checking enabled build and check.  This triggered failures
in the gcc.target/riscv/save-restore* tests.  We are using XINT to access an
XWINT value; INTVAL is the preferred solution.

	gcc/
	* config/riscv/riscv-sr.c (riscv_sr_match_prologue): Use INTVAL
	instead of XINT.