imxfb: correct location of callbacks in suspend and resume

The probe function passes a pointer to a struct fb_info to
platform_set_drvdata(), so don't interpret the return value of
platform_get_drvdata() as a pointer to struct imxfb_info.

The original imxfb_info *fbi backlight_power was NULL but in imxfb_suspend
it was 4 resulting in an oops as imxfb_suspend calls
imxfb_disable_controller(fbi) which in turn has

	if (fbi->backlight_power)
			fbi->backlight_power(0);

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Acked-by: Sascha Hauer <kernel@pengutronix.de>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>