Handle source data alignment correctly in Blit32to32SurfaceAlphaAltivec().

  Fixes Bugzilla #279.

--HG--
branch : SDL-1.2
extra : convert_revision : svn%3Ac70aab31-4412-0410-b14c-859654838e24/branches/SDL-1.2%402259

src/video/SDL_blit_A.c

@@ -1287,7 +1287,7 @@ static void Blit32to32SurfaceAlphaAltivec(SDL_BlitInfo *info)
         ONE_PIXEL_BLEND((UNALIGNED_PTR(dstp)) && (width), width);
         if (width > 0) {
             int extrawidth = (width % 4);
-            vector unsigned char valigner = vec_lvsl(0, srcp);
+            vector unsigned char valigner = VEC_ALIGNER(srcp);
             vector unsigned char vs = (vector unsigned char)vec_ld(0, srcp);
             width -= extrawidth;
             while (width) {