testsuite: Fix dg directives order in arm/aarch64 vml[as]_float_not_fused.c

dg-do must come before dg-skip-if, this patch fixes this oversight in
these two tests.

2021-05-03  Christophe Lyon  <christophe.lyon@linaro.org>

	gcc/testsuite/
	* gcc.target/aarch64/advsimd-intrinsics/vmla_float_not_fused.c:
	Fix dg directives order.
	* gcc.target/aarch64/advsimd-intrinsics/vmls_float_not_fused.c:
	Likewise.