nuc900/rtc: change the waiting for device ready implement

nuc900/rtc: change the waiting for device ready implement

- add an mdelay(1) to the polling loop to cause less frequent access to
  the hardware register.

- change the return value from ENODEV to EPERM if the loop timed out.  I
  think the 'Operation not permitted' description is more suitable for the
  meaning of 'check_rtc_access_enable()' function, it just be used to
  judge rtc access operation is permitted or not.

Signed-off-by: Wan ZongShun <mcuos.com@gmail.com>
Cc: Alessandro Zummo <a.zummo@towertech.it>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>