docs(analytics, ios): fix on-device-conversion variable name

[mikehardy]

Description

Tiny typo fix

Related issues

#6325
#6321
#6264

Release Summary

just a doc change

Checklist

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
  • Yes
• My change supports the following platforms;
  • Android
  • iOS
• My change includes tests;
  • e2e tests added or updated in packages/\*\*/e2e
  • jest tests added or updated in packages/\*\*/__tests__
• I have updated TypeScript types that are affected by my change.
• This is a breaking change;
  • Yes
  • No

Test Plan

---

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Name	Status	Preview	Updated
react-native-firebase	✅ Ready (Inspect)	Visit Preview	Jun 22, 2022 at 3:55PM (UTC)

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[codecov]

Codecov Report

Merging #6331 (2fa87a6) into main (7affa79) will decrease coverage by 28.66%.
The diff coverage is n/a.

❗ Current head 2fa87a6 differs from pull request most recent head f8b9a3d. Consider uploading reports for the commit f8b9a3d to get more accurate results

@@              Coverage Diff              @@
##               main    #6331       +/-   ##
=============================================
- Coverage     54.50%   25.84%   -28.65%     
=============================================
  Files           208       97      -111     
  Lines         10356     4289     -6067     
  Branches       1645     1048      -597     
=============================================
- Hits           5643     1108     -4535     
+ Misses         4432     2581     -1851     
- Partials        281      600      +319