RISC-V: Fix warning in riscv.md

RISC-V: Fix warning in riscv.md

Notice there is warning:
../../../riscv-gcc/gcc/config/riscv/riscv.md:1356:32: warning:
comparison between signed and unsigned integer expressions
[-Wsign-compare]
       if (INTVAL (operands[2]) == GET_MODE_MASK (HImode))
../../../riscv-gcc/gcc/config/riscv/riscv.md:1358:37: warning:
comparison between signed and unsigned integer expressions
[-Wsign-compare]
       else if (INTVAL (operands[2]) == GET_MODE_MASK (SImode))
../../../riscv-gcc/gcc/config/riscv/riscv.md: In function ‘rtx_def*
gen_anddi3(rtx, rtx, rtx)’:
../../../riscv-gcc/gcc/config/riscv/riscv.md:1356:32: warning:
comparison between signed and unsigned integer expressions
[-Wsign-compare]
       if (INTVAL (operands[2]) == GET_MODE_MASK (HImode))
../../../riscv-gcc/gcc/config/riscv/riscv.md:1358:37: warning:
comparison between signed and unsigned integer expressions
[-Wsign-compare]
       else if (INTVAL (operands[2]) == GET_MODE_MASK (SImode))

Add unsigned conversion to fix this warning.

Signed-off-by: Juzhe-Zhong <juzhe.zhong@rivai.ai>
gcc/ChangeLog:

	* config/riscv/riscv.md: Fix signed and unsigned comparison
	warning.