common: convolve: Use memcpy in av1_highbd_convolve_2d_copy_sr_c

Use memcpy() function instead of copying 16-bit integers serially.

Change-Id: Ia42dbc3eff36bdb526fdad429104879537a05ae5
diff --git a/av1/common/convolve.c b/av1/common/convolve.c
index 798bc76..56f9db1 100644
--- a/av1/common/convolve.c
+++ b/av1/common/convolve.c
@@ -550,9 +550,7 @@
   (void)bd;
 
   for (int y = 0; y < h; ++y) {
-    for (int x = 0; x < w; ++x) {
-      dst[y * dst_stride + x] = src[y * src_stride + x];
-    }
+    memcpy(dst + y * dst_stride, src + y * src_stride, w * sizeof(src[0]));
   }
 }