Replace aom_malloc with aom_memalign

This fixes a segfault in nightly tests for 32-bit clang builds.

Change-Id: Ie6de357443bc5bc5f3180791f34fce2566c242a9
diff --git a/av1/encoder/pickrst.c b/av1/encoder/pickrst.c
index dbedc23..37b0f1a 100644
--- a/av1/encoder/pickrst.c
+++ b/av1/encoder/pickrst.c
@@ -1174,7 +1174,7 @@
 
   assert(ntiles[1] <= ntiles[0]);
   RestUnitSearchInfo *rusi =
-      (RestUnitSearchInfo *)aom_malloc(sizeof(*rusi) * ntiles[0]);
+      (RestUnitSearchInfo *)aom_memalign(16, sizeof(*rusi) * ntiles[0]);
 
   RestSearchCtxt rsc;
   for (int plane = AOM_PLANE_Y; plane <= AOM_PLANE_V; ++plane) {