rtc: fix module reference count in rtc-proc

rtc-proc.c is not built as a module. Thus, rather than dealing with
THIS_MODULE's reference count, we should deal with rtc->owner's
reference count.

Signed-off-by: Geliang Tang <geliangtang@163.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>