qcacld-3.0: p2p: Replace fallthrough comment with attribute

-Wimplicit-fallthrough is being enabled by default. Some compilers
such as clang require the attribute instead of just a fallthrough comment.

Change-Id: Ie800ea60a4e12deff2ba2b0462de70e2b252082d
CRs-Fixed: 3217411

components/p2p/core/src/wlan_p2p_main.c

@@ -1410,7 +1410,7 @@ QDF_STATUS p2p_status_connect(struct wlan_objmgr_vdev *vdev)
 		 * since no scan before 4-way handshake and
 		 * won't enter state P2P_CLIENT_CONNECTING_STATE_2:
 		 */
-		/* fallthrough */
+		fallthrough;
 	case P2P_CLIENT_CONNECTING_STATE_2:
 		p2p_status_update(p2p_soc_obj,
 				  P2P_CLIENT_COMPLETED_STATE);