drivers/i2c/tpm: Fix error handling for tis structure not initialized

If the TPM completely fails to respond then the vendor structure may not
have assigned handlers yet, so catch that case and return error so the
boot can continue to recovery mode instead of asserting over and over.

Change-Id: If3a11567df89bc73b4d4878bf89d877974044f34
Signed-off-by: Duncan Laurie <dlaurie@chromium.org>
Reviewed-on: https://review.coreboot.org/16416
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
Tested-by: build bot (Jenkins)
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>

src/drivers/i2c/tpm/tis.c

@@ -114,6 +114,9 @@ static ssize_t tpm_transmit(const uint8_t *buf, size_t bufsiz)
 	memcpy(&ordinal, buf + TPM_CMD_ORDINAL_BYTE, sizeof(ordinal));
 	ordinal = be32_to_cpu(ordinal);
 
+	if (!chip->vendor.send || !chip->vendor.status || !chip->vendor.cancel)
+		return -1;
+
 	if (count == 0) {
 		printk(BIOS_DEBUG, "tpm_transmit: no data\n");
 		return -1;