hpfs_unlink() calls permission() prior to truncating the file. HPFS
doesn't define a .permission method, so replace with explicit call to
generic_permission().
This is equivalent, except that devcgroup_inode_permission() and
security_inode_permission() are not called.
The truncation is just an implementation detail of the unlink, so
these security checks are unnecessary.
I suspect that even calling generic_permission() is unnecessary, since
we shouldn't mind if the file isn't writable. But I leave that to the
maintainer to decide.