RISC-V: Adjust testcase asm check for vx-[5|6]-i[8|16].c

After commit 9f8409f2e2c, SLP discovery can retry swapped operands for
commutative parents before falling back to an external scalar.
These tests can be vectorized again, so update asm check.

gcc/testsuite/ChangeLog:

	* gcc.target/riscv/rvv/autovec/vx_vf/vx-5-i16.c: Expect vadd.vx,
	vmul.vx, vsadd.vx and vssub.vx.
	* gcc.target/riscv/rvv/autovec/vx_vf/vx-5-i8.c: Likewise.
	* gcc.target/riscv/rvv/autovec/vx_vf/vx-6-i16.c: Likewise.
	* gcc.target/riscv/rvv/autovec/vx_vf/vx-6-i8.c: Likewise.

Signed-off-by: Zhongyao Chen <chen.zhongyao@zte.com.cn>