kernel: mempool: Remove unnecessary condition check
kernel: mempool: Remove unnecessary condition check

Removing an unnecessary check in k_mem_pool_alloc. The condition is
already being checked in the if.

MISRA-C rule 14.3

Signed-off-by: Flavio Ceolin <979b9165500b0741b9d0500e2efd74fc1547bff7@intel.com>

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