Don't use dp for lock icon padding

We don't want it to scale with density
changes. It scales in the wrong direction.

This was also causing a difference in lock icon size for foldable
devices where the inner display is using a different lock icon padding
than the outer display.

Test: visual manual inspection
Fixes: 259677170
Fixes: 264738021
Change-Id: I4075fd5e3f0aec7472edc56a0f8c95be5e68d65a