cachefiles: unmark inode in use in error path

In the Linux kernel, the following vulnerability has been resolved:

cachefiles: unmark inode in use in error path

Unmark inode in use if error encountered. If the in-use flag leakage
occurs in cachefiles_open_file(), Cachefiles will complain "Inode
already in use" when later another cookie with the same index key is
looked up.

If the in-use flag leakage occurs in cachefiles_create_tmpfile(), though
the "Inode already in use" warning won't be triggered, fix the leakage
anyway.