msdosfs: handle inconsistently hashed denodes

It is possible, on the corrupted msdosfs volume, to have file which
denode inode number does not match the one calculated using directory
cluster. Instead of asserting the condition as impossible, handle it
and return error, after reclaiming the aliased vnode.

In collaboration with: pho
Reviewed by: markj, mckusick
Sponsored by: The FreeBSD Foundation
MFC after: 1 week
Differential revision: https://reviews.freebsd.org/D33721