drm/mst: use DP_GET_SINK_COUNT() for sink count in ESI

Take bit 7 into account when reading sink count from
DP_DEVICE_SERVICE_IRQ_VECTOR_ESI0.
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220104184857.784563-2-jani.nikula@intel.com

drivers/gpu/drm/drm_dp_mst_topology.c

@@ -4196,7 +4196,7 @@ int drm_dp_mst_hpd_irq(struct drm_dp_mst_topology_mgr *mgr, u8 *esi, bool *handl
 	int ret = 0;
 	int sc;
 	*handled = false;
-	sc = esi[0] & 0x3f;
+	sc = DP_GET_SINK_COUNT(esi[0]);
 
 	if (sc != mgr->sink_count) {
 		mgr->sink_count = sc;