tests: crypto: cbc_mode: Fix input length
tests: crypto: cbc_mode: Fix input length

Input length was accounting TC_AES_BLOCK_SIZE twice and consequently
not considering the whole cipher.

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

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