sws: disable yuv2rgb warning for planar rgb.

planar rgb formats do not use the table
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libswscale/yuv2rgb.c

@@ -919,7 +919,8 @@ av_cold int ff_yuv2rgb_c_init_tables(SwsContext *c, const int inv_table[4],
         break;
     default:
         c->yuvTable = NULL;
-        av_log(c, AV_LOG_ERROR, "%ibpp not supported by yuv2rgb\n", bpp);
+        if(!isPlanar(c->dstFormat) || bpp<=24)
+            av_log(c, AV_LOG_ERROR, "%ibpp not supported by yuv2rgb\n", bpp);
         return -1;
     }
     return 0;