tpm: Unify the send callback behaviour

The send() callback should never return length as it does not in every
driver except tpm_crb in the success case. The reason is that the main
transmit functionality only cares about whether the transmit was
successful or not and ignores the count completely.

Suggested-by: Stefan Berger <stefanb@linux.ibm.com>
Cc: stable@vger.kernel.org
Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Reviewed-by: Stefan Berger <stefanb@linux.ibm.com>
Reviewed-by: Jerry Snitselaar <jsnitsel@redhat.com>
Tested-by: Alexander Steffen <Alexander.Steffen@infineon.com>