tpm: vtpm_proxy: Suppress error logging when in closed state

Suppress the error logging when the core TPM driver sends commands
to the VTPM proxy driver and -EPIPE is returned in case the VTPM
proxy driver is 'closed' (closed anonymous file descriptor).  This
error code is only returned by the send function and by tpm_transmit
when the VTPM proxy driver is being used.

Signed-off-by: Stefan Berger <stefanb@linux.vnet.ibm.com>
Reviewed-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Tested-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>