Fix build failure when ACPI_VIDEO=m and SAMSUNG_LAPTOP=y.
The patch prevents that specific config combination.

drivers/built-in.o: In function `samsung_init':
samsung-laptop.c:(.init.text+0x128ff): undefined reference to `acpi_video_unregister'
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Reported-by: Randy Dunlap <rdunlap@infradead.org>
Reported-by: Fengguang Wu <fengguang.wu@intel.com>
Cc: Corentin Chary <corentin.chary@gmail.com>

build testing:
ACPI_VIDEO=m, SAMSUNG_LAPTOP=m: OK
ACPI_VIDEO=y, SAMSUNG_LAPTOP=m: OK
ACPI_VIDEO=y, SAMSUNG_LAPTOP=y: OK
ACPI=n, SAMSUNG_LAPTOP=y: OK
ACPI=n, SAMSUNG_LAPTOP=m: OK
Signed-off-by: Matthew Garrett <matthew.garrett@nebula.com>