lib: mmutest: Use MOVN instead of NEG in mmutest_arch_store_uint32 am: bf18683601

Original change: https://android-review.googlesource.com/c/trusty/lk/trusty/+/2795816

Change-Id: Ie53dedda1a2684bf98470dd4ecb0fbe3e16e43e0
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>