drm: Don't return 0 for a value used as a denominator

Static analysis will be unhappy if a function can theoretically return
0 and we're trying to divide by that value.

Mark that case that cannot occur as a BUG() instead.
Signed-off-by: Damien Lespiau <damien.lespiau@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/drm_dp_mst_topology.c

@@ -1772,7 +1772,7 @@ static int drm_dp_get_vc_payload_bw(int dp_link_bw, int dp_link_count)
 	case DP_LINK_BW_5_4:
 		return 10 * dp_link_count;
 	}
-	return 0;
+	BUG();
 }
 
 /**