swscale: fix 15- and 16-bits RGB conversions

This is tested with X11 and should fix LP#665298.

This partially reverts commit fb7f0141.
RV24 is left as is because I cannot test it on my GPU.
(cherry picked from commit 37e37fb1)

modules/codec/avcodec/chroma.c

@@ -98,8 +98,8 @@ static const struct
     VLC_RGB( VLC_FOURCC('R','G','B','4'), PIX_FMT_RGB4, PIX_FMT_BGR4, 0x10, 0x06, 0x01 )
     VLC_RGB( VLC_FOURCC('R','G','B','8'), PIX_FMT_RGB8, PIX_FMT_BGR8, 0xC0, 0x38, 0x07 )
 
-    VLC_RGB( VLC_CODEC_RGB15, PIX_FMT_BGR555, PIX_FMT_RGB555, 0x7c00, 0x03e0, 0x001f )
-    VLC_RGB( VLC_CODEC_RGB16, PIX_FMT_BGR565, PIX_FMT_RGB565, 0xf800, 0x07e0, 0x001f )
+    VLC_RGB( VLC_CODEC_RGB15, PIX_FMT_RGB555, PIX_FMT_BGR555, 0x7c00, 0x03e0, 0x001f )
+    VLC_RGB( VLC_CODEC_RGB16, PIX_FMT_RGB565, PIX_FMT_BGR565, 0xf800, 0x07e0, 0x001f )
     VLC_RGB( VLC_CODEC_RGB24, PIX_FMT_BGR24, PIX_FMT_RGB24, 0xff0000, 0x00ff00, 0x0000ff )
 
     VLC_RGB( VLC_CODEC_RGB32, PIX_FMT_RGB32, PIX_FMT_BGR32, 0x00ff0000, 0x0000ff00, 0x000000ff )