include/drivers: Fix docs on z_clock_set_timeout()
include/drivers: Fix docs on z_clock_set_timeout()

This wasn't explained correctly.  The tick convention we use here
(owing to the way legacy code was written) is a little weird.  Timeout
delays are passed in a "round down" sense, so that setting a timeout
in "one tick" means that the interrupt will arrive anywhere between
zero and one ticks in the future.

Signed-off-by: Andy Ross <c70f9a6bf6ee0cd69c8af4ce5e6b131945769315@intel.com>

galak/zephyr,Vudentz/zephyr,Vudentz/zephyr,punitvara/zephyr,explora26/zephyr,Vudentz/zephyr,zephyrproject-rtos/zephyr,explora26/zephyr,nashif/zephyr,zephyrproject-rtos/zephyr,nashif/zephyr,explora26/zephyr,Vudentz/zephyr,punitvara/zephyr,zephyrproject-rtos/zephyr,GiulianoFranchetto/zephyr,ldts/zephyr,Vudentz/zephyr,galak/zephyr,finikorg/zephyr,explora26/zephyr,finikorg/zephyr,galak/zephyr,ldts/zephyr,zephyrproject-rtos/zephyr,nashif/zephyr,nashif/zephyr,GiulianoFranchetto/zephyr,galak/zephyr,nashif/zephyr,ldts/zephyr,ldts/zephyr,GiulianoFranchetto/zephyr,punitvara/zephyr,galak/zephyr,punitvara/zephyr,explora26/zephyr,ldts/zephyr,finikorg/zephyr,GiulianoFranchetto/zephyr,Vudentz/zephyr,punitvara/zephyr,GiulianoFranchetto/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,finikorg/zephyr