Make staking keeper passing more idiomatic

[ValarDragon]

The whole point of the keepers.go refactor was to make the keeper on the app a pointer =)
See line 142, app.StakingKeeper = &stakingKeeper. This just makes this section cleaner

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For contributor use:

• Targeted PR against correct branch (see CONTRIBUTING.md)
• Updated relevant documentation (docs/) or specification (x/<module>/spec/) - N/A
• Added a relevant changelog entry to the Unreleased section in CHANGELOG.md - N/A
• Re-reviewed Files changed in the Github PR explorer

[codecov-commenter]

Codecov Report

Merging #742 (36e702f) into main (bc65a83) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main     #742   +/-   ##
=======================================
  Coverage   18.73%   18.73%           
=======================================
  Files         172      172           
  Lines       23908    23908           
=======================================
  Hits         4478     4478           
  Misses      18655    18655           
  Partials      775      775           

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