Keep old timestamps during data migration

As part of the update to patch_set_approavals, the category names
are changed. Doing so causes "ON UPDATE CURRENT_TIMESTAMP" in at
least MySQL to replace all of the existing timestamps with the
time of the migration. Since the purpose of CURRENT_TIMESTAMP
here is to track when the approval vote happened, this is a loss
of data.

Amend the data migration to include granted=granted in the update
list so that anyone running the migration will not lose their
data.

Change-Id: If80891018eae0fab75770a5aea5a382200e9112f