RISC-V: Adjust the scan asm for v[sz]ext.vf2 for v1 and v12

The previous match v1 may match the v12 as well, therefore
add the non-num boundary.

gcc/testsuite/ChangeLog:

	* gcc.target/riscv/rvv/autovec/group_overlap/vsext_vf2-i16-m1.c:
	* gcc.target/riscv/rvv/autovec/group_overlap/vsext_vf2-i16-m2.c:
	* gcc.target/riscv/rvv/autovec/group_overlap/vsext_vf2-i16-m4.c:
	* gcc.target/riscv/rvv/autovec/group_overlap/vsext_vf2-i16-mf2.c:
	* gcc.target/riscv/rvv/autovec/group_overlap/vsext_vf2-i16-mf4.c:
	* gcc.target/riscv/rvv/autovec/group_overlap/vsext_vf2-i32-m1.c:
	* gcc.target/riscv/rvv/autovec/group_overlap/vsext_vf2-i32-m2.c:
	* gcc.target/riscv/rvv/autovec/group_overlap/vsext_vf2-i32-mf2.c:
	* gcc.target/riscv/rvv/autovec/group_overlap/vsext_vf2-i8-m1.c:
	* gcc.target/riscv/rvv/autovec/group_overlap/vsext_vf2-i8-m2.c:
	* gcc.target/riscv/rvv/autovec/group_overlap/vsext_vf2-i8-mf2.c:
	* gcc.target/riscv/rvv/autovec/group_overlap/vsext_vf2-i8-mf4.c:
	* gcc.target/riscv/rvv/autovec/group_overlap/vsext_vf2-i8-mf8.c:

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