Fixed typo on line 75 of nni/nas/pytorch/mutables.py

[ankitaggarwal23]

Description

This Pull Request fixes a typo on line 75 of nni/nas/pytorch/mutables.py.

While I was reading the source code, I wondered whether this is a typo, as shown below:

nni/nas/pytorch/mutables.py, line 75

@property
71    def name(self):
72        """
73        After the search space is parsed, it will be the module name of the mutable.
74        """
75        return self._name if hasattr(self, "_name") else "_key"

Should "_key" be self._key because this method is supposed to return a key/name of a mutable?

The Issue seems to be very minor but it improves the readability of the Code and fixes a typo online 75 of nni/nas/pytorch/mutables.pyissue in Python 3 which happens to be a standard.

I'm a First-Time Contributor to Microsoft Open-Source so it would be helpful for me understanding how PR workflow works and help me step up in future contributions as well.

Fixes: #3515

@ultmaster @liuzhe-lz Can you review this PR and let me know?

[Lijiaoa]

target to v2.2 or master?