RISC-V: Reconcile the existing test due to cost model change

RISC-V: Reconcile the existing test due to cost model change

The cost model change will make the default cost of vx to 2, thus
reconcile the asm check for this change.

gcc/testsuite/ChangeLog:

	* gcc.target/riscv/rvv/autovec/sat/vec_sat_u_sub_trunc-1-u16.c:
	Update the asm check due to cost model change.
	* gcc.target/riscv/rvv/autovec/sat/vec_sat_u_sub_trunc-1-u32.c:
	Diito.
	* gcc.target/riscv/rvv/autovec/sat/vec_sat_u_sub_trunc-1-u8.c:
	Ditto.

Signed-off-by: Pan Li <pan2.li@intel.com>