Allocate cm->cdef_info.srcbuf on 16-byte alignment

In av1_alloc_cdef_linebuf(), allocate cm->cdef_info.srcbuf with 16-byte
alignment because av1_cdef_frame() will pass cm->cdef_info.srcbuf as the
'src' argument to cdef_fb_row(), and some pointer in that buffer will
eventually be passed to _mm_load_si128(), whose input "must be aligned
on a 16-byte boundary or a general-protection exception may be
generated."

BUG=aomedia:3025

Change-Id: Iab614da9affff1608e52d20f6406a1b8ebfe80df

av1/common/alloccommon.c

diff --git a/av1/common/alloccommon.c b/av1/common/alloccommon.c
index 442973d..39aed89 100644
--- a/av1/common/alloccommon.c
+++ b/av1/common/alloccommon.c
@@ -114,7 +114,7 @@
   if (cm->cdef_info.srcbuf == NULL)
     CHECK_MEM_ERROR(
         cm, cm->cdef_info.srcbuf,
-        aom_malloc(sizeof(*cm->cdef_info.srcbuf) * CDEF_INBUF_SIZE));
+        aom_memalign(16, sizeof(*cm->cdef_info.srcbuf) * CDEF_INBUF_SIZE));
 
   for (int plane = 0; plane < num_planes; plane++) {
     const int shift = plane == AOM_PLANE_Y ? 0 : cm->seq_params.subsampling_x;