drivers/video/backlight/lm3630_bl.c: remove ret = -EIO of lm3630_backlight_register()

There is no need to return -EIO, because backlight_device_register()
already returns correct error values.

Signed-off-by: Jingoo Han <jg1.han@samsung.com>
Acked-by: Daniel Jeong <daniel.jeong@ti.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>