drivers/rtc/rtc-omap.c: fix a memory leak

request_mem_region() will call kzalloc to allocate memory for struct
resource.  release_resource() unregisters the resource but does not free
the allocated memory, thus use release_mem_region() instead to fix the
memory leak.

Also add a missing iounmap() in omap_rtc_remove().

Signed-off-by: Axel Lin <axel.lin@gmail.com>
Cc: Alessandro Zummo <a.zummo@towertech.it>
Cc: Sekhar Nori <nsekhar@ti.com>
Cc: Kevin Hilman <khilman@deeprootsystems.com>
Cc: Tony Lindgren <tony@atomide.com>
Acked-by: Mark A. Greer <mgreer@mvista.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>