VAAPI: relax assert() it was to stringent and only let H264 pass.

Some codecs need less surfaces then 30. Relax the assert() to allow
other HW codecs too work too.

modules/codec/avcodec/vaapi.c

@@ -125,7 +125,7 @@ static int Open( vlc_va_vaapi_t *p_va, int i_codec_id, int i_count )
 
     int i_needed = __MAX(i_surface_count, i_count);
     i_surface_count += i_needed;
-    assert( i_surface_count >= 30 );
+    assert( i_surface_count >= 23 );
 
     /* */
     memset( p_va, 0, sizeof(*p_va) );