swtpm: Initialize ptm_est type to avoid uninitialized bytes

swtpm: Initialize ptm_est type to avoid uninitialized bytes

Valgrind complains about uninitialized bytes being accessed by a writev()
call in libfuse. It points to a line in the error branch
'error_not_running', but the error does not seem to come from there.
Instead, if we initialize ptm_est to zeros the problem goes away.

Signed-off-by: Stefan Berger <stefanb@linux.vnet.ibm.com>