serial: mctrl_gpio: Fix passing zero to 'ERR_PTR' warning

drivers/tty/serial/serial_mctrl_gpio.c:214
 mctrl_gpio_init() warn: passing zero to 'ERR_PTR'

gpiod_to_irq() never return 0, so remove the useless test
and make code more clear.

Reviewed-by: Jiri Slaby <jirislaby@kernel.org>
Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Link: https://lore.kernel.org/r/20201031030530.1304-1-yuehaibing@huawei.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/serial_mctrl_gpio.c

@@ -207,7 +207,7 @@ struct mctrl_gpios *mctrl_gpio_init(struct uart_port *port, unsigned int idx)
 			continue;
 
 		ret = gpiod_to_irq(gpios->gpio[i]);
-		if (ret <= 0) {
+		if (ret < 0) {
 			dev_err(port->dev,
 				"failed to find corresponding irq for %s (idx=%d, err=%d)\n",
 				mctrl_gpios_desc[i].name, idx, ret);