TPM: chip disabled state erronously being reported as error

tpm_do_selftest() attempts to read a PCR in order to
decide if one can rely on the TPM being used or not.
The function that's used by __tpm_pcr_read() does not
expect the TPM to be disabled or deactivated, and if so,
reports an error.

It's fine if the TPM returns this error when trying to
use it for the first time after a power cycle, but it's
definitely not if it already returned success for a
previous attempt to read one of its PCRs.

The tpm_do_selftest() was modified so that the driver only
reports this return code as an error when it really is.

Reported-and-tested-by: Paul Bolle <pebolle@tiscali.nl>
Cc: Stable <stable@vger.kernel.org>
Signed-off-by: Rajiv Andrade <srajiv@linux.vnet.ibm.com>