fix(module: picker): fix picker style error

[fisherspy]

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 #434 into master will increase coverage by 0.05%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #434      +/-   ##
==========================================
+ Coverage   85.72%   85.77%   +0.05%     
==========================================
  Files         314      314              
  Lines        7623     7623              
  Branches     1082     1082              
==========================================
+ Hits         6535     6539       +4     
+ Misses        661      655       -6     
- Partials      427      429       +2

Impacted Files	Coverage Δ
components/picker/picker.component.ts	69.69% <0%> (+1.51%)	⬆️
components/picker/picker.service.ts	85% <0%> (+5%)	⬆️

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