tpm_tis: make ilb_base_addr static

The pointer ilb_base_addr does not need to be in global scope, so make
it static.

Cleans up sparse warning:
"symbol 'ilb_base_addr' was not declared. Should it be static?"

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Reviewed-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Signed-off-by: James Morris <james.l.morris@oracle.com>