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

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

Since commit 6de39c773b52b277 ("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 8aba87e1320a50f5 ("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.be
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>