Fix double low power ticker interrupt
Fix double low power ticker interrupt

When computing the next set_interrupt time in the common ticker layer
the absolute time in microseconds is rounded down to the closes low
power tick. Because of this the low power ticker interrupt fires one
cycle too early. This causes ticker_irq_handler to run even though
there are no events ready to run.

To prevent this unnecessary interrupt this patch changes the
computation for the next set_interrupt time to round up rather than
down.

mbedmicro/mbed,kjbracey-arm/mbed,mbedmicro/mbed,betzw/mbed-os,kjbracey-arm/mbed,andcor02/mbed-os,c1728p9/mbed-os,c1728p9/mbed-os,kjbracey-arm/mbed,mbedmicro/mbed,betzw/mbed-os,c1728p9/mbed-os,kjbracey-arm/mbed,betzw/mbed-os,betzw/mbed-os,betzw/mbed-os,andcor02/mbed-os,c1728p9/mbed-os,andcor02/mbed-os,c1728p9/mbed-os,andcor02/mbed-os,mbedmicro/mbed,andcor02/mbed-os,mbedmicro/mbed,c1728p9/mbed-os,andcor02/mbed-os,betzw/mbed-os