tpm: suppress durations sysfs output if not set

[Stefan Berger <stefanb@linux.vnet.ibm.com>]

Suppress the output of durations if they were not read during driver 
initialization.
This is similar to other sysfs entries that return nothing if for some 
reason sending the commands to the TPM fails.

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

---
  drivers/char/tpm/tpm.c |    3 +++
  1 file changed, 3 insertions(+)

Index: linux-2.6/drivers/char/tpm/tpm.c
===================================================================
--- linux-2.6.orig/drivers/char/tpm/tpm.c
+++ linux-2.6/drivers/char/tpm/tpm.c
@@ -963,6 +963,9 @@ ssize_t tpm_show_durations(struct device
  {
      struct tpm_chip *chip = dev_get_drvdata(dev);

+    if (chip->vendor.duration[TPM_LONG] == 0)
+        return 0;
+
      return sprintf(buf, "%d %d %d [%s]\n",
                 jiffies_to_usecs(chip->vendor.duration[TPM_SHORT]),
                 jiffies_to_usecs(chip->vendor.duration[TPM_MEDIUM]),