tpm/tpm_ftpm_tee: fix struct ftpm_tee_private documentation

tpm/tpm_ftpm_tee: fix struct ftpm_tee_private documentation

The `state` member in `struct ftpm_tee_private` is in the documentation,
but it has never been in the implementation since the commit 09e574831b27
("tpm/tpm_ftpm_tee: A driver for firmware TPM running inside TEE") that
introduced it.

Remove it to have a match between documentation and implementation.

Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org>
Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>