tpm/vtpm: fix kdoc warnings

Use corret kdoc format for function description and eliminate warning
of type:

tpm_ibmvtpm.c:66: warning: No description found for parameter 'count'

Signed-off-by: Tomas Winkler <tomas.winkler@intel.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>