uncrypt: package on non-data partition should follow the right path

Fix the accidental change of behavior in [1]. OTA packages not on /data
partition should still go through the path that has validity checks and
wipe_misc() steps.

[1]: commit eaf33654.

Change-Id: I3e86e19f06603bfe6ecc691c9aa66a8a8a79c5fb
(cherry picked from commit fb4ccef1)