drm: Make drm_dp_mst_dsc_aux_for_port() safe for old compilers

Older compilers either want two extra pairs of curly braces around the
initializer for local variable desc, or they want a single pair of curly
braces with nothing inside.  Because current Linux-kernel practice favors
the latter, this commit makes it so.
Suggested-by: NChris Wilson <chris@chris-wilson.co.uk>
Suggested-by: NJoe Perches <joe@perches.com>
Suggested-by: NChristoph Hellwig <hch@infradead.org>
Signed-off-by: NPaul E. McKenney <paulmck@kernel.org>

drivers/gpu/drm/drm_dp_mst_topology.c

@@ -5494,7 +5494,7 @@ struct drm_dp_aux *drm_dp_mst_dsc_aux_for_port(struct drm_dp_mst_port *port)
 {
 	struct drm_dp_mst_port *immediate_upstream_port;
 	struct drm_dp_mst_port *fec_port;
-	struct drm_dp_desc desc = { 0 };
+	struct drm_dp_desc desc = { };
 	u8 endpoint_fec;
 	u8 endpoint_dsc;