The function hptiop_iop_request_callback_itl does not need to be in
global scope, so make it static.

Cleans up sparse warning:
"symbol 'hptiop_iop_request_callback_itl' was not declared. Should it
 be static?"
Signed-off-by: NColin Ian King <colin.king@canonical.com>
Signed-off-by: NMartin K. Petersen <martin.petersen@oracle.com>