Simplify logic in cdrom_release() without semantic change.

Signed-off-by: Borislav Petkov <bbpetkov@yahoo.de>
Cc: Jens Axboe <jens.axboe@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>