fa-mobile should be aligned at the center

[luixxiul]

Describe the issue you encountered:
On about:preferences#payments, click "add funds" to open the modal dialog.

fa-mobile is not aligned at the center

Expected behavior:
It should be aligned at the center like this:

• Brave Version: master branch

• Any related issues: Refactor about:preferences#payments followups #6047

[luixxiul]

Test plan:

Open about:preferences#payments
Click Add funds
Make sure the phone icon is aligned at the center of the row