blackfin RTC driver: if we dont define irq_set_freq, the common rtc-dev layer...

blackfin RTC driver: if we dont define irq_set_freq, the common rtc-dev layer will give us the same behavior of returning ENOTTY

Signed-off-by: Mike Frysinger <michael.frysinger@analog.com>
Signed-off-by: Bryan Wu <bryan.wu@analog.com>
Signed-off-by: Bryan Wu <cooloney@kernel.org>
Cc: David Brownell <david-b@pacbell.net>
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>