Fix accessibility_display_magnification_scale restore

accessibility_display_magnification_scale has a default value set, so
the current check to see if it was already configured during restore
always falsely returned true. Now, we compare it to the default value
and only say it's configured if different from the default.

Bug: 72737403
Test: 1) Manual d2d restore:
a) Set non-default value on source -> correctly restores on target
b) Default value on source -> correctly has default value on target
c) Set non-default value in SUW during restore -> correctly does not
override with value from source
2) Unit: atest SettingsHelperRestoreTest

Change-Id: Ie0670aac7b4ce806ac7b8baef4eb15a7c40d5919