cortex_m_systick: fix _timer_cycle_get_32() race

We need to account for the interrupt happening in the middle
of the calculation.

Issue: ZEP-1546
Change-Id: I193534856d7521cac7ca354d3e5b65e93b984bb1
Signed-off-by: Andrew Boie <andrew.p.boie@intel.com>
1 file changed