Alignment is required for sad_array8

For at least some of the implementations of sdx8f, such as
vpx_sad4x4x8_sse4_1, aligned moves are used to move the results into the
array.

Change-Id: I83df5a8e657b44e906d0d8b0bc154f1e5660f7f9

vp8/encoder/mcomp.c

@@ -1591,7 +1591,6 @@ int vp8_full_search_sadx8(MACROBLOCK *x, BLOCK *b, BLOCKD *d, int_mv *ref_mv,
     int col_min = ref_col - distance;
     int col_max = ref_col + distance;
 
-    // TODO(johannkoenig): check if this alignment is necessary.
     DECLARE_ALIGNED(16, unsigned int, sad_array8[8]);
     unsigned int sad_array[3];