Update mlc_llm.rst correcting for mlc from mlc_llm

[agrajagco]

Fixed verify installation command line from mlc_llm to mlc (fails when attempting to use mlc_llm). Verified actual installed module is mlc as shown below.

(mlc-prebuilt) agrajag@tor-orin:/opt/miniconda3/envs/mlc-prebuilt/lib/python3.11/site-packages/mlc$ ls -la
total 16
drwxrwxr-x  3 agrajag agrajag 4096 Apr  6 20:59 .
drwxrwxr-x 13 agrajag agrajag 4096 Apr  6 20:59 ..
-rw-rw-r--  1 agrajag agrajag   15 Apr  6 20:59 __init__.py
drwxrwxr-x  2 agrajag agrajag 4096 Apr  6 20:59 __pycache__
(mlc-prebuilt) agrajag@tor-orin:/opt/miniconda3/envs/mlc-prebuilt/lib/python3.11/site-packages/mlc$ python -c "import mlc; print(mlc)"
<module 'mlc' from '/opt/miniconda3/envs/mlc-prebuilt/lib/python3.11/site-packages/mlc/__init__.py'>