ice: fix return value check in ice_gnss.c

kthread_create_worker() and tty_alloc_driver() return ERR_PTR()
and never return NULL. The NULL test in the return value check
should be replaced with IS_ERR().

Fixes: 43113ff ("ice: add TTY for GNSS module for E810T device")
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
Tested-by: Gurucharan <gurucharanx.g@intel.com> (A Contingent worker at Intel)
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>

drivers/net/ethernet/intel/ice/ice_gnss.c

@@ -125,7 +125,7 @@ static struct gnss_serial *ice_gnss_struct_init(struct ice_pf *pf)
 	 * writes.
 	 */
 	kworker = kthread_create_worker(0, "ice-gnss-%s", dev_name(dev));
-	if (!kworker) {
+	if (IS_ERR(kworker)) {
 		kfree(gnss);
 		return NULL;
 	}
@@ -253,7 +253,7 @@ static struct tty_driver *ice_gnss_create_tty_driver(struct ice_pf *pf)
 	int err;
 
 	tty_driver = tty_alloc_driver(1, TTY_DRIVER_REAL_RAW);
-	if (!tty_driver) {
+	if (IS_ERR(tty_driver)) {
 		dev_err(ice_pf_to_dev(pf), "Failed to allocate memory for GNSS TTY\n");
 		return NULL;
 	}