clock_control: nrf5: Return -EBUSY on turning off if still in use
clock_control: nrf5: Return -EBUSY on turning off if still in use

Fix return value to -EBUSY instead of 0 when releasing a
reference but not physically turning off the clock.

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

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