tests/p4wq: Fix impossible sleep interval
tests/p4wq: Fix impossible sleep interval

The code here was written to "get out of the way just long enough for
the trivial context switch and callback to execute".  But on a machine
with 50 kHz ticks, that's not reliably enough time and this was
failing spuriously.  Which would have been a reasonably forgivable
mistake to make had I not written this code with this very machine in
mind...

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

galak/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,Vudentz/zephyr,Vudentz/zephyr,galak/zephyr,Vudentz/zephyr,zephyrproject-rtos/zephyr,nashif/zephyr,finikorg/zephyr,finikorg/zephyr,Vudentz/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr,nashif/zephyr,nashif/zephyr,galak/zephyr,Vudentz/zephyr,galak/zephyr,nashif/zephyr,finikorg/zephyr,nashif/zephyr,zephyrproject-rtos/zephyr,Vudentz/zephyr