drivers/rtc/rtc-r9701.c: avoid second call to rtc_valid_tm()

r9701_get_datetime() calls rtc_valid_tm() and returns the value returned
by rtc_valid_tm(), which can be used in the `if', so calling
rtc_valid_tm() a second time is not required.

Signed-off-by: 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>