rtc: rtc-sh - 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.

Signed-off-by: Axel Lin <axel.lin@gmail.com>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>