fix(module: input-item): fix input-item value protect

[nuonuoge]

PR Checklist

Please check if your PR fulfills the following requirements:

• The commit message follows our guidelines: https://github.com/NG-ZORRO/ng-zorro-antd-mobile/blob/master/CONTRIBUTING.md#commit
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

[x] Bugfix
[ ] Feature
[ ] Code style update (formatting, local variables)
[ ] Refactoring (no functional changes, no api changes)
[ ] Build related changes
[ ] CI related changes
[ ] Documentation content changes
[ ] Application (the showcase website) / infrastructure changes
[ ] Other... Please describe:

What is the current behavior?

Issue Number: N/A

What is the new behavior?

Does this PR introduce a breaking change?

[ ] Yes
[x] No

Other information

[codecov]

Codecov Report

Merging #196 into master will decrease coverage by 0.02%.
The diff coverage is 100%.

@@            Coverage Diff            @@
##           master    #196      +/-   ##
=========================================
- Coverage   86.33%   86.3%   -0.03%     
=========================================
  Files         222     222              
  Lines        7162    7162              
  Branches     1003    1003              
=========================================
- Hits         6183    6181       -2     
- Misses        583     584       +1     
- Partials      396     397       +1

Impacted Files	Coverage Δ
components/input-item/input-item.component.ts	95.18% <100%> (ø)	⬆️
.../input-item/custom-input/custom-input.component.ts	90.84% <0%> (-1.41%)	⬇️

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