swscale: Fix compilation with --disable-mmx2.

Some MMX2 functions were being referenced without proper #ifdefs.

libswscale/x86/swscale_mmx.c

@@ -182,6 +182,8 @@ void ff_sws_init_swScale_mmx(SwsContext *c)
 
     if (cpu_flags & AV_CPU_FLAG_MMX)
         sws_init_swScale_MMX(c);
+#if HAVE_MMX2
     if (cpu_flags & AV_CPU_FLAG_MMX2)
         sws_init_swScale_MMX2(c);
+#endif
 }

libswscale/x86/yuv2rgb_mmx.c

@@ -72,12 +72,14 @@ SwsFunc ff_yuv2rgb_init_mmx(SwsContext *c)
         c->srcFormat != PIX_FMT_YUVA420P)
         return NULL;
 
-    if (HAVE_MMX2 && cpu_flags & AV_CPU_FLAG_MMX2) {
+#if HAVE_MMX2
+    if (cpu_flags & AV_CPU_FLAG_MMX2) {
         switch (c->dstFormat) {
         case PIX_FMT_RGB24:  return yuv420_rgb24_MMX2;
         case PIX_FMT_BGR24:  return yuv420_bgr24_MMX2;
         }
     }
+#endif
 
     if (HAVE_MMX && cpu_flags & AV_CPU_FLAG_MMX) {
         switch (c->dstFormat) {