drivers/rtc/rtc-cmos.c: fix compilation warning when !CONFIG_PM_SLEEP

CONFIG_PM will be set also if only CONFIG_PM_RUNTIME is set which causes
the compiler to emit following warning:

  drivers/rtc/rtc-cmos.c:845:12: warning: =E2=80=98cmos_resume=E2=80=99 defined but not used [-Wunused-function]

Fix this by using CONFIG_PM_SLEEP instead of CONFIG_PM and removing it
from the driver pm ops as this has been taken care by
SIMPLE_DEV_PM_OPS() already.

Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>