staging: rtl8188eu: Remove unneeded cast

Fix Coccinelle alert:

drivers/staging//rtl8188eu/os_dep/usb_intf.c:336:13-27: WARNING: casting value returned by memory allocation function to (struct adapter *) is useless.

This issue was detected by using the Coccinelle software.
Signed-off-by: Christopher Diaz Riveros <chrisadr@gentoo.org>
Acked-by: Larry Finger <Larry.Finger@lwfinger.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/rtl8188eu/os_dep/usb_intf.c

@@ -333,7 +333,7 @@ static struct adapter *rtw_usb_if1_init(struct dvobj_priv *dvobj,
 	struct net_device *pmondev;
 	int status = _FAIL;
 
-	padapter = (struct adapter *)vzalloc(sizeof(*padapter));
+	padapter = vzalloc(sizeof(*padapter));
 	if (padapter == NULL)
 		goto exit;
 	padapter->dvobj = dvobj;