Fix int 32 amplitude storer

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What has been done:

Checklist

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• Versioning and website
  • Changelog is up to date
  • The patch number in parameters.F90 is correct
  • Updates (if any) to the website have been added
• Testing
  • Tested with -rcheck
  • Tested with -fbatch
• Compliance with style guide
  • Do's and dont's
  • Documentation style