MX1/MX2: -EINVAL overwritten in second iteration in mxc_gpio_setup_multiple_pins()

Due to the `ret = gpio_request()' below in the loop, the initial -EINVAL value
of ret is overwritten.

Signed-off-by: Roel Kluin <roel.kluin@gmail.com>
Acked-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>