xpt_create_path() requires mfi_io_lock to be held, so do it.

mfi(4) doesn't panic on host startup now.

MFC this if svn 249468-242726 is shoveled back to stable/9

Obtained from:	Yahoo! Inc.

sys/dev/mfi/mfi_cam.c

@@ -318,13 +318,16 @@ mfip_cam_rescan(struct mfi_softc *sc, uint32_t tid)
 	}
 
 	sim = camsc->sim;
+	mtx_lock(&sc->mfi_io_lock);
 	if (xpt_create_path(&ccb->ccb_h.path, NULL, cam_sim_path(sim),
 	    tid, CAM_LUN_WILDCARD) != CAM_REQ_CMP) {
 		xpt_free_ccb(ccb);
+		mtx_unlock(&sc->mfi_io_lock);
 		device_printf(sc->mfi_dev,
 		    "Cannot create path for bus rescan.\n");
 		return;
 	}
+	mtx_unlock(&sc->mfi_io_lock);
 
 	xpt_rescan(ccb);