cxl/core/port: Fix NULL but dereferenced coccicheck error

Fix the following coccicheck warning:
./drivers/cxl/core/port.c:913:21-24: ERROR: port is NULL but dereferenced.

The put_device() is only relevent in the is_cxl_root() case.

Fixes: 2703c16c ("cxl/core/port: Add switch port enumeration")
Signed-off-by: Wan Jiabing <wanjiabing@vivo.com>
Link: https://lore.kernel.org/r/20220307094158.404882-1-wanjiabing@vivo.comSigned-off-by: Dan Williams <dan.j.williams@intel.com>

drivers/cxl/core/port.c

@@ -911,7 +911,10 @@ static void cxl_detach_ep(void *data)
 			break;
 
 		port = find_cxl_port(dport_dev);
-		if (!port || is_cxl_root(port)) {
+		if (!port)
+			continue;
+
+		if (is_cxl_root(port)) {
 			put_device(&port->dev);
 			continue;
 		}