staging: r8188eu: Fix smatch warning in hal/usb_ops_linux.c

Smatch reports the following warning:
drivers/staging/rtl8188eu/hal/usb_ops_linux.c:614 usb_read_port() warn: variable dereferenced before check 'precvbuf' (see line 611)

Fixing this particular warning required some refactoring of the code.
Signed-off-by: Larry Finger <Larry.Finger@lwfinger.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/rtl8188eu/hal/usb_ops_linux.c

@@ -605,13 +605,18 @@ _func_enter_;
 		return _FAIL;
 	}
 
+	if (!precvbuf) {
+		RT_TRACE(_module_hci_ops_os_c_, _drv_err_,
+			 ("usb_read_port:precvbuf==NULL\n"));
+		return _FAIL;
+	}
+
 	if ((!precvbuf->reuse) || (precvbuf->pskb == NULL)) {
 		precvbuf->pskb = skb_dequeue(&precvpriv->free_recv_skb_queue);
 		if (NULL != precvbuf->pskb)
 			precvbuf->reuse = true;
 	}
 
-	if (precvbuf != NULL) {
 	rtl8188eu_init_recvbuf(adapter, precvbuf);
 
 	/* re-assign for linux based on skb */
@@ -664,11 +669,6 @@ _func_enter_;
 			err, purb->status);
 		ret = _FAIL;
 	}
-	} else {
-		RT_TRACE(_module_hci_ops_os_c_, _drv_err_,
-			 ("usb_read_port:precvbuf ==NULL\n"));
-		ret = _FAIL;
-	}
 
 _func_exit_;
 	return ret;