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 <[e-mail]>
Signed-off-by: YueHaibing <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/tty/serial/serial_mctrl_gpio.c

···
 			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);