vboot: clear tpm when required

Function which invoked when TPM clear is requested was left empty,
this patch fixes it.

BRANCH=gru
BUG=chrome-os-partner:57411
TEST=verified on a chromeos device that tpm is in fact cleared when
     CLEAR_TPM_OWNER_REQUEST is set by userland.

Change-Id: I4370792afd512309ecf7f4961ed4d44a04a3e2aa
Signed-off-by: Vadim Bendebury <vbendeb@chromium.org>
Reviewed-on: https://review.coreboot.org/16805
Tested-by: build bot (Jenkins)
Reviewed-by: Philipp Deppenwiese <zaolin.daisuki@googlemail.com>

src/vboot/secdata_tpm.c

@@ -154,6 +154,7 @@ static uint32_t _factory_initialize_tpm(struct vb2_context *ctx)
 uint32_t tpm_clear_and_reenable(void)
 {
 	VBDEBUG("TPM: Clear and re-enable\n");
+	RETURN_ON_FAILURE(tlcl_force_clear());
 	return TPM_SUCCESS;
 }