init/reboot: call MNT_FORCE at the last umount(2)

The last one will avoid errors=panic in ext4.

Bug: 63981945
Bug: 65481582
Change-Id: I9c86afcce441767e24fc43668ab1ff6230155a9f
Merged-In: I9c86afcce441767e24fc43668ab1ff6230155a9f
Signed-off-by: Jaegeuk Kim <jaegeuk@google.com>
(cherry picked from commit 0f04f72c2de2f5c42e62f23306bc106dddcdabb1)
1 file changed