samples: arch: mpu_test: Update Readme.
samples: arch: mpu_test: Update Readme.

Update the readme for mpu_test sample to contain
correct sample outputs for mpu read, write and run operations.

Signed-off-by: Aastha Grover <ae5900957a378b2cd4ba2c8b72e8e30cc5f9a938@intel.com>

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