Fix interim return variable name when DH enabled

[gojimmypi]

Description

Please describe the scope of the fix or feature addition.

When using a user_settings.h such as this one that turns on DH with #define HAVE_DH, the Espressif TLS Client example currently fails to compile.

.../IDE/Espressif/ESP-IDF/examples/wolfssl_client/main/client-tls.c:300:5: error: 'ret' undeclared (first use in this function)
  300 |     ret = wolfSSL_CTX_SetMinDhKey_Sz(ctx, (word16)minDhKeyBits);
      |     ^~~

The example otherwise works with the user_settings.h that it has.

This is related to coming up with a common user_settings.h in the template example that will be copied to the published Espressif wolfSSL Managed Component.

I do have major updates to the Espressif examples and cmake files, not ready for PR.

Fixes zd# n/a

Testing

How did you test?

Tested only on Espressif platform.

Checklist

• added tests
• updated/added doxygen
• updated appropriate READMEs
• Updated manual and documentation