drivers/rtc/rtc-r9701.c: check that r9701_set_datetime() succeeded

When the driver detects that the clock time is invalid, it attempts to
write a sane time into the hardware.  We curently assume that everything
is OK if those writes succeeded.  But it is better to re-read the time
from the hardware to ensure that the new settings got there OK.

Cc: Devendra Naga <devendra.aaru@gmail.com>
Cc: Alessandro Zummo <a.zummo@towertech.it>
Cc: Anatolij Gustschin <agust@denx.de>
Cc: Andreas Dumberger <andreas.dumberger@tqs.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>