rtc-isl1208: fix double removal of a sysfs entry

Signed-off-by: Alessandro Zummo <a.zummo@towertech.it>
Cc: Herbert Valerio Riedel <hvr@gnu.org>
Cc: Hartley Sweeten <hartleys@visionengravers.com>
Cc: David Brownell <david-b@pacbell.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>