cifs: fix double free on failed kerberos auth

If session setup failed with kerberos auth, we ended up freeing
cifs_ses::auth_key.response twice in SMB2_auth_kerberos() and
sesInfoFree().

Fix this by zeroing out cifs_ses::auth_key.response after freeing it
in SMB2_auth_kerberos().

Fixes: a4e430c8

 ("cifs: replace kfree() with kfree_sensitive() for sensitive data")
Signed-off-by: Paulo Alcantara (SUSE) <pc@cjr.nz>
Acked-by: Ronnie Sahlberg <lsahlber@redhat.com>
Signed-off-by: Steve French <stfrench@microsoft.com>