logging: fix signed and unsigend comparison warnings
logging: fix signed and unsigend comparison warnings

Fix instances of:
warning: comparison between signed and unsigned integer expressions
[-Wsign-compare]

Signed-off-by: Joakim Andersson <cf0fcab5d38d6e132e92a97bcb0bae257abf4936@nordicsemi.no>

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