Decoder: Remove unnecssary optimization while setting MV context

Few MV cabac contexts were being used as WORD16 pointers
but were not guaranteed to be aligned to 2 byte boundary.

Bug: 33073518
Test: Tested with -fsanitize=alignment enabled on avcdec

Change-Id: I294179d6ec37b0f1d9cbe093b1f9780f036a9cb8
1 file changed