Initial return value of connectToServerWithBackoffRetries in the tls_mutual_auth example is set incorrectly (CA-358)

[MochiButter]

Description

The function connectToServerWithBackoffRetries in the file mqtt_demo_mutual_auth.c has its initial return status incorrectly set to EXIT_SUCCESS. In situations where the tls connection fails, the program continues as if it was successful, returning EXIT_SUCCESS. In order for the back off retries to function, this must be set to EXIT_FAILURE.

Testing

Tested with esp-idf version ESP-IDF v5.2.5-30-g41c2b799ad
I can see the example message on the aws IoT test client.

Without this change, turning off the wifi access point during the demo doesn't trigger the backoff retries when trying to connect. With this change, the increasing times between retries can be seen in the console.

[CLAassistant]

All committers have signed the CLA.