Fix errors in hpe specific get methods (#7952)
* Fix errors in hpe specific get methods
* corrects reference to non existent `self.chassis_uri_list` to
`self.chassis_uris`
* corrects syntactically incorrect dereferences
* removes an uneccessary variable assignment to `chassis_uri_list`
in `get_psu_inventory` method
* adds changelog fragment for above indicating fix of issue #7951
* Update changelog.
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Co-authored-by: Felix Fontein <felix@fontein.de>
(cherry picked from commit dd7c3ad10d)
Co-authored-by: Dave Rawks <dave@rawks.io>
