tpm: Clean up error reporting in tpm_init_tpmdev()

tpm: Clean up error reporting in tpm_init_tpmdev()

Calling error_report() in a function that takes an Error ** argument
is suspicious.  tpm_init_tpmdev() does that, and then fails without
setting an error.  Its caller main(), via tpm_init() and
qemu_opts_foreach(), is fine with it, but clean it up anyway.

Cc: Stefan Berger <stefanb@linux.vnet.ibm.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Stefan Berger <stefanb@linux.ibm.com>
Message-Id: <20181017082702.5581-30-armbru@redhat.com>