backlight/gpio_backlight: Compare against struct fb_info.device

backlight/gpio_backlight: Compare against struct fb_info.device

Struct gpio_backlight_platform_data refers to a platform device within
the Linux device hierarchy. The test in gpio_backlight_check_fb()
compares it against the fbdev device in struct fb_info.dev, which
is different. Fix the test by comparing to struct fb_info.device.

Fixes a bug in the backlight driver and prepares fbdev for making
struct fb_info.dev optional.

v2:
	* move renames into separate patch (Javier, Sam, Michael)

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Fixes: 8b770e3c9824 ("backlight: Add GPIO-based backlight driver")
Cc: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Cc: Rich Felker <dalias@libc.org>
Cc: John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>
Cc: Lee Jones <lee@kernel.org>
Cc: Daniel Thompson <daniel.thompson@linaro.org>
Cc: Jingoo Han <jingoohan1@gmail.com>
Cc: linux-sh@vger.kernel.org
Cc: dri-devel@lists.freedesktop.org
Cc: <stable@vger.kernel.org> # v3.12+
Reviewed-by: Sam Ravnborg <sam@ravnborg.org>
Reviewed-by: Daniel Thompson <daniel.thompson@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20230613110953.24176-4-tzimmermann@suse.de