efika: Fix board id detection

Current code is assuming that gpio_get_value() is returning 0 or 1 but it
should be checking if the value is 0 or not. Not doing it properly is breaking
the detection of the board (and thus the reboot of efika mx to2) when using
the new mxc gpio driver, which relies on basic mmio gpio.

Signed-off-by: Arnaud Patard <arnaud.patard@rtp-net.org>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>