staging: r8188eu: Fix smatch warning in os_dep/osdep_service.c

Smatch reports the following warning:
drivers/staging/rtl8188eu/os_dep/osdep_service.c:634 rtw_change_ifname() warn: variable dereferenced before check 'padapter' (see line 630)

The dereference in question is deferred until the validity of 'padapter' is verified.
Signed-off-by: NLarry Finger <Larry.Finger@lwfinger.net>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/rtl8188eu/os_dep/osdep_service.c

@@ -627,13 +627,14 @@ void rtw_free_netdev(struct net_device *netdev)
 int rtw_change_ifname(struct adapter *padapter, const char *ifname)
 {
 	struct net_device *pnetdev;
-	struct net_device *cur_pnetdev = padapter->pnetdev;
+	struct net_device *cur_pnetdev;
 	struct rereg_nd_name_data *rereg_priv;
 	int ret;
 
 	if (!padapter)
 		goto error;
 
+	cur_pnetdev = padapter->pnetdev;
 	rereg_priv = &padapter->rereg_nd_name_priv;
 
 	/* free the old_pnetdev */