rtc: mxc: fix memory leak

Free pdata before exit.  Found by cppcheck.

[yuasa@linux-mips.org: add missing iounmap()]
Signed-off-by: Alexander Beregalov <a.beregalov@gmail.com>
Reviewed-by: WANG Cong <xiyou.wangcong@gmail.com>
Acked-by: Daniel Mack <daniel@caiaq.de>
Acked-by: Alessandro Zummo <a.zummo@towertech.it>
Cc Yoichi Yuasa <yuasa@linux-mips.org>
Cc: Paul Gortmaker <p_gortmaker@yahoo.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>