imx: ventana: Avoid undefined behaviour

imx: ventana: Avoid undefined behaviour

The leds array within struct ventana has space for 3 elements, but the
setup_board_gpio() function tries to set up 4 GPIOs for LEDs. Recent
versions of GCC complain about that:

	board/gateworks/gw_ventana/gw_ventana.c: In function 'setup_board_gpio':
	board/gateworks/gw_ventana/gw_ventana.c:987:27: warning: iteration 3u invokes undefined behavior [-Waggressive-loop-optimizations]
	   if (gpio_cfg[board].leds[i])
				   ^
	board/gateworks/gw_ventana/gw_ventana.c:986:2: note: containing loop
	  for (i = 0; i < 4; i++) {
	  ^

Fix this by making the upper bound of the loop match the array size.

Signed-off-by: Thierry Reding <treding@nvidia.com>
Acked-by: Tim Harvey <tharvey@gateworks.com>