staging: rtl8723bs: Remove unneeded cast

Fix Coccinelle alert:

drivers/staging//rtl8723bs/os_dep/sdio_intf.c:340:13-27: 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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/rtl8723bs/os_dep/sdio_intf.c

@@ -337,7 +337,7 @@ static struct adapter *rtw_sdio_if1_init(struct dvobj_priv *dvobj, const struct
 	struct adapter *padapter = NULL;
 	PSDIO_DATA psdio = &dvobj->intf_data;
 
-	padapter = (struct adapter *)vzalloc(sizeof(*padapter));
+	padapter = vzalloc(sizeof(*padapter));
 	if (padapter == NULL) {
 		goto exit;
 	}