s390-ccw: force diag 308 subcode to unsigned long

s390-ccw: force diag 308 subcode to unsigned long

We currently pass an integer as the subcode parameter. However,
the upper bits of the register containing the subcode need to
be 0, which is not guaranteed unless we explicitly specify the
subcode to be an unsigned long value.

Fixes: d046c51dad3 ("pc-bios/s390-ccw: Get device address via diag 308/6")
Cc: [email protected]
Signed-off-by: Cornelia Huck <[email protected]>
Acked-by: Christian Borntraeger <[email protected]>
Tested-by: Thomas Huth <[email protected]>
Signed-off-by: Thomas Huth <[email protected]>