[SCSI] atari_NCR5380: Provide a dummy NCR5380_exit()

and call it from atari_scsi_release(), cfr. the other NCR5380 drivers.

This fixes:

drivers/scsi/NCR5380.h:303: warning: ‘NCR5380_exit’ declared ‘static’ but never defined

Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>