serial: mxs-auart: Don't check for mctrl_gpio_to_gpiod() returning error

Since commit 1d267ea6 ("serial: mctrl-gpio: simplify init
routine"), mctrl_gpio_init() returns failure if the assignment to any
member of the gpio array results in an error pointer.
Since commit c359522194593815 ("serial: mctrl_gpio: Avoid probe failures
in case of missing gpiolib"), mctrl_gpio_to_gpiod() returns NULL in the
!CONFIG_GPIOLIB case.
Hence there is no longer a need to check for mctrl_gpio_to_gpiod()
returning an error value.  A simple NULL check is sufficient.

This follows the spirit of commit 445df7ff ("serial: mctrl-gpio:
drop usages of IS_ERR_OR_NULL") in the mctrl-gpio core.
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/20190814092924.13857-3-geert+renesas@glider.beSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/mxs-auart.c

@@ -969,10 +969,8 @@ static int mxs_auart_dma_init(struct mxs_auart_port *s)
 
 }
 
-#define RTS_AT_AUART()	IS_ERR_OR_NULL(mctrl_gpio_to_gpiod(s->gpios,	\
-							UART_GPIO_RTS))
-#define CTS_AT_AUART()	IS_ERR_OR_NULL(mctrl_gpio_to_gpiod(s->gpios,	\
-							UART_GPIO_CTS))
+#define RTS_AT_AUART()	!mctrl_gpio_to_gpiod(s->gpios, UART_GPIO_RTS)
+#define CTS_AT_AUART()	!mctrl_gpio_to_gpiod(s->gpios, UART_GPIO_CTS)
 static void mxs_auart_settermios(struct uart_port *u,
 				 struct ktermios *termios,
 				 struct ktermios *old)