auxdisplay: ht16k33: Connect backlight to fbdev

Currently /sys/class/graphics/fb0/bl_curve is not accessible (-ENODEV),
as the driver does not connect the backlight to the frame buffer device.
Fix this moving backlight initialization up, and filling in
fb_info.bl_dev.

Fixes: 8992da44 ("auxdisplay: ht16k33: Driver for LED controller")
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Reviewed-by: Robin van der Gracht <robin@protonic.nl>
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>