vaapi: use proper official fourcc constants

libva will never return I420 fourcc code, instead it uses IYUV. The first image format returned by vaQueryImageFormat with Intel VA backend is YV12, so using I420 wasn't an issue.
Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>

modules/codec/avcodec/vaapi.c

@@ -354,9 +354,9 @@ static int CreateSurfaces( vlc_va_sys_t *sys, void **pp_hw_ctx, vlc_fourcc_t *pi
     vlc_fourcc_t  i_chroma = 0;
     for( int i = 0; i < i_fmt_count; i++ )
     {
-        if( p_fmt[i].fourcc == VA_FOURCC( 'Y', 'V', '1', '2' ) ||
-            p_fmt[i].fourcc == VA_FOURCC( 'I', '4', '2', '0' ) ||
-            p_fmt[i].fourcc == VA_FOURCC( 'N', 'V', '1', '2' ) )
+        if( p_fmt[i].fourcc == VA_FOURCC_YV12 ||
+            p_fmt[i].fourcc == VA_FOURCC_IYUV ||
+            p_fmt[i].fourcc == VA_FOURCC_NV12 )
         {
             if( vaCreateImage(  sys->p_display, &p_fmt[i], i_width, i_height, &sys->image ) )
             {
@@ -465,10 +465,10 @@ static int Extract( vlc_va_t *va, picture_t *p_picture, void *opaque,
         return VLC_EGENERIC;
 
     const uint32_t i_fourcc = sys->image.format.fourcc;
-    if( i_fourcc == VA_FOURCC('Y','V','1','2') ||
-        i_fourcc == VA_FOURCC('I','4','2','0') )
+    if( i_fourcc == VA_FOURCC_YV12 ||
+        i_fourcc == VA_FOURCC_IYUV )
     {
-        bool b_swap_uv = i_fourcc == VA_FOURCC('I','4','2','0');
+        bool b_swap_uv = i_fourcc == VA_FOURCC_IYUV;
         uint8_t *pp_plane[3];
         size_t  pi_pitch[3];
 
@@ -485,7 +485,7 @@ static int Extract( vlc_va_t *va, picture_t *p_picture, void *opaque,
     }
     else
     {
-        assert( i_fourcc == VA_FOURCC('N','V','1','2') );
+        assert( i_fourcc == VA_FOURCC_NV12 );
         uint8_t *pp_plane[2];
         size_t  pi_pitch[2];