ANDROID: mnt: Fix freeing of mount data

Fix double free on error paths

Signed-off-by: Daniel Rosenberg <drosen@google.com>
Change-Id: I1c25a175e87e5dd5cafcdcf9d78bf4c0dc3f88ef
Bug: 65386954
Fixes: c9b3c8159e5c ("mnt: Add filesystem private data to mount points")