ecryptfs: initialize new auth_tokens before teardown

ecryptfs_destroy_mount_crypt_stat() checks whether each
auth_tok->global_auth_tok_key is nonzero and if so puts that key.  However,
in some early mount error paths nothing has initialized the pointer, and we
try to key_put() garbage.  Running the bad cipher tests in the testsuite
exposes this, and it's happy with the following change.

Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Cc: Michael Halcrow <mhalcrow@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>