tty:serial:mvebu-uart:fix a wrong return

in this place, the function should return a
negative value and the PTR_ERR already returns
a negative,so return -PTR_ERR() is wrong.
Signed-off-by: Ntangbin <tangbin@cmss.chinamobile.com>
Cc: stable <stable@vger.kernel.org>
Acked-by: NJiri Slaby <jslaby@suse.cz>
Link: https://lore.kernel.org/r/20200305013823.20976-1-tangbin@cmss.chinamobile.comSigned-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/mvebu-uart.c

@@ -851,7 +851,7 @@ static int mvebu_uart_probe(struct platform_device *pdev)
 
 	port->membase = devm_ioremap_resource(&pdev->dev, reg);
 	if (IS_ERR(port->membase))
-		return -PTR_ERR(port->membase);
+		return PTR_ERR(port->membase);
 
 	mvuart = devm_kzalloc(&pdev->dev, sizeof(struct mvebu_uart),
 			      GFP_KERNEL);