Fix face/fingerprint consent primary footer button logic

Currently, the primary footer button on the face and fingerprint enroll
consent pages reads "I agree" even before the user has scrolled to the
bottom of the screen. This commit fixes the issue so that "More" is
displayed until the user scrolls to the bottom. The remaining logic is
left intact.

Test: Manual:
1. Start face or fingerprint enrollment
2. Confirm primary button shows "More" and secondary button is hidden
3. Press the "More" button or scroll to the bottom of the screen
4. Ensure primary button shows "I agree" and secondary shows "No thanks"

Fixes: 189268868
Change-Id: I02fa47d1de83bd5b5d82c733495ae579cbd2d6c6