drivers: flash: nrf: Fix ticker stop synchronization
drivers: flash: nrf: Fix ticker stop synchronization

Fix usage fault due to spurious ticker timeout expiry post
enqueuing of ticker stop operation.

Use ticker operation callback to handle completion of ticker
stop operation and then give the semaphore to thread to
notifying the completion of flash operation.

Signed-off-by: Vinayak Kariappa Chettimada <e780c9f87dc729ad454f47292ad82c8652353064@nordicsemi.no>

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