Fix DDP normalization type check logic

[Mr-Neutr0n]

Summary

• Fix inverted condition in DDP normalization check
• Correct 'inst' to 'instance' in error message

Problem

The current code raises an error when norm == 'syncbatch':

if self.opt.norm == "syncbatch":
    raise ValueError(...)

This is the opposite of the intended behavior. The code should raise an error when norm is NOT 'syncbatch' or 'instance'.

Solution

Changed the condition to:

if self.opt.norm != "syncbatch" and self.opt.norm != "instance":
    raise ValueError(...)

Also fixed the error message to reference 'instance' instead of 'inst' for clarity.

Test plan

• Run DDP training with --norm syncbatch
• Run DDP training with --norm instance
• Verify error is raised for other norm types (e.g., 'batch')

Fixes #1709