drm/i915: acpi/video.c fix section mismatch warning

Currently acpi_video_exit() is exported as well as using __exit which causes:

  WARNING: drivers/acpi/video.o(__ksymtab+0x0): Section mismatch in reference from the variable __ksymtab_acpi_video_exit to the function .exit.text:acpi_video_exit()
  The symbol acpi_video_exit is exported and annotated __exit
  Fix this by removing the __exit annotation of acpi_video_exit or drop the export.

Signed-off-by: Jaswinder Singh Rajput <jaswinderrajput@gmail.com>
Signed-off-by: Len Brown <len.brown@intel.com>