logging: init strdup mem_slab with aligned buffer size
logging: init strdup mem_slab with aligned buffer size

We are using a non-32-bit aligned value as the block size
when initializing the strdup mem_slab for Logger.

When the non-aligned pointer is being freed, it's converted
to a u32_t and this generates the following:
***** USAGE FAULT *****
  Unaligned memory access

Let's use the aligned buffer size as the block size instead.

Signed-off-by: Michael Scott <a17fed27eaa842282862ff7c1b9c8395a26ac320@foundries.io>

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