ARM: mach-mx35_3ds: Fix build warning due to the lack of 'const' annotation

Fix the following build warning:

arch/arm/mach-imx/mach-mx35_3ds.c: In function 'mx35_3ds_lcd_set_power':
arch/arm/mach-imx/mach-mx35_3ds.c:112: warning: passing argument 2 of 'gpiochip_find' from incompatible pointer type
include/asm-generic/gpio.h:145: note: expected 'int (*)(struct gpio_chip *, const void *)' but argument is of type 'int (*)(struct gpio_chip *, void *)'

Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>