drm/tegra: dc: Return planar flag for non-YUV modes

This prevents the compiler from warning about using a variable that is
possibly uninitialized.
Signed-off-by: NThierry Reding <treding@nvidia.com>

drivers/gpu/drm/tegra/dc.c

@@ -134,6 +134,9 @@ static bool tegra_dc_format_is_yuv(unsigned int format, bool *planar)
 		return true;
 	}
 
+	if (planar)
+		*planar = false;
+
 	return false;
 }