tomoyo: Use sensible time interface

There is no point in calling gettimeofday if only the seconds part of
the timespec is used. Use get_seconds() instead. It's not only the
proper interface it's also faster.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Cc: John Stultz <john.stultz@linaro.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Kentaro Takeda <takedakn@nttdata.co.jp>
Cc: linux-security-module@vger.kernel.org
Link: http://lkml.kernel.org/r/20140611234607.775273584@linutronix.de