rtc: mc13xxx: remove __exit_p()

Since we no longer allow building without hotplug, the
mc13xxx_rtc_remove() function is always present and we should not use
__exit_p() to refer to it.

Signed-off-by: Alexander Shiyan <shc_work@mail.ru>
Cc: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Cc: Sascha Hauer <kernel@pengutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>