net: lwm2m: fix error message in load_tls_credential()
net: lwm2m: fix error message in load_tls_credential()

Copy/paste issue was showing the wrong error message when a TLS
credential failed to be added.

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

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