control/media_descriptor.c: Fix memcpy usage.

src/control/media_descriptor.c

@@ -117,7 +117,7 @@ libvlc_media_descriptor_duplicate( libvlc_media_descriptor_t *p_md_orig )
     libvlc_media_descriptor_t * p_md;
 
     p_md = malloc( sizeof(libvlc_media_descriptor_t) );
-    memcpy( p_md_orig, p_md, sizeof(libvlc_media_descriptor_t) );
+    memcpy( p_md, p_md_orig, sizeof(libvlc_media_descriptor_t) );
 
     return p_md;
 }