logging: Prevent redundant thread wake up
logging: Prevent redundant thread wake up

Fix a bug introduced by 658123bb21 where if all backends were
ready prior to logging thread loop, thread was periodically
waken up for no reason. Fix is setting timeout to K_FOREVER
if all backends are ready after the initialization.

Signed-off-by: Krzysztof Chruscinski <9b6dc988558c51b0405b49b55c8e66862969844b@nordicsemi.no>

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