aarch64/testsuite: Fix gcc.target/aarch64/simd/vmmla.c [PR116207]

After r15-2414-g2d105efd6f60 which fixed the dg-do directive, the testcase
stopped working because there was a missing -save-temps. This adds that and
now the testcase passes again.

Pushed as obvious.

gcc/testsuite/ChangeLog:

	PR testsuite/116207
	* gcc.target/aarch64/simd/vmmla.c: Add -save-temps to the
	options.

Signed-off-by: Andrew Pinski <quic_apinski@quicinc.com>