arm64: looprestoration: Avoid unnecessary alignment of the mid buffer

There's no gain in aligning it to more than 16 bytes. The ALIGN_STK_32
macro actually only aligns to 16 bytes on arm targets anyway.

src/arm/looprestoration_init_tmpl.c

@@ -66,7 +66,7 @@ static void wiener_filter_neon(pixel *const dst, const ptrdiff_t dst_stride,
                                const int w, const int h, const int16_t fh[7],
                                const int16_t fv[7], const enum LrEdgeFlags edges)
 {
-    ALIGN_STK_32(int16_t, mid, 68 * 384,);
+    ALIGN_STK_16(int16_t, mid, 68 * 384,);
     int mid_stride = (w + 7) & ~7;
 
     // Horizontal filter