Add helper function to get data module for llava

[hemildesai]

Just extracts data module definition to a helper function.

[github-actions]

beep boop 🤖: 🚨 The following files must be fixed before merge!

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Your code was analyzed with PyLint. The following annotations have been identified:

************* Module nemo.collections.vlm.api
nemo/collections/vlm/api.py:1:0: C0116: Missing function or method docstring (missing-function-docstring)

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Your code has been rated at 9.74/10

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Mitigation guide:

• Add sensible and useful docstrings to functions and methods
• For trivial methods like getter/setters, consider adding # pylint: disable=C0116 inside the function itself
• To disable multiple functions/methods at once, put a # pylint: disable=C0116 before the first and a # pylint: enable=C0116 after the last.

By applying these rules, we reduce the occurance of this message in future.

Thank you for improving NeMo's documentation!