Timer interrupt should be raised at the same cycle when CCOUNT equals
CCOMPARE. As cycles are counted in batches, timer interrupt is sent
every time CCOMPARE lies in the interval [old CCOUNT, new CCOUNT]. This
is wrong, because when new CCOUNT equals CCOMPARE interrupt is sent
twice, once for the upper interval boundary and once for the lower. Fix
that by excluding lower interval boundary from the condition.

This doesn't have user-visible effect, because CCOMPARE reload always
causes CCOUNT increment followed by current timer interrupt reset.

Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>