tpm: replace symbolic permission with octal for securityfs files

checkpatch.pl flags warning for symbolic permissions and suggests
to replace with octal value.

This patch changes securityfs pseudo files permission
to octal values in tpm_bios_log_setup().

Signed-off-by: Nayna Jain <nayna@linux.vnet.ibm.com>
Reviewed-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Tested-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>