fix(AutoComplete): add missing backfill prop in type

[zhanba]

First of all, thank you for your contribution! :-)

Please makes sure that these checkboxes are checked before submitting your PR, thank you!

• [*] Make sure that you propose PR to right branch: bugfix for master, feature for latest active branch feature-x.x.
• [*] Make sure that you follow antd's code convention.
• [*] Run npm run lint and fix those errors before submitting in order to keep consistent code style.
• [*] Rebase before creating a PR to keep commit history clear.
• [*] Add some descriptions and refer relative issues for you PR.

Extra checklist:

if isBugFix :

• [*] Make sure that you add at least one unit test for the bug which you had fixed.

elif isNewFeature :

• Update API docs for the component.
• Update/Add demo to demonstrate new feature.
• Update TypeScript definition for the component.
• Add unit tests for the feature.

[ant-design-bot]

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[codecov]

Codecov Report

Merging #10909 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master   #10909   +/-   ##
=======================================
  Coverage   91.59%   91.59%           
=======================================
  Files         194      194           
  Lines        4769     4769           
  Branches     1329     1329           
=======================================
  Hits         4368     4368           
  Misses        397      397           
  Partials        4        4

Impacted Files	Coverage Δ
components/auto-complete/index.tsx	87.17% <ø> (ø)	⬆️

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