rtc/nuc900: make returning time checking function valid

Make returning time checking function valid.  In spite of using the
'rtc_valid_tm', nevertheless, the read time function omits its returning
value, that means the 'rtc_valid_tm' is useless here.

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>