isci: fix "no outbound task timeout" default value

The default should be 5us.  The hardware encodes it in 256ns increments,
so the value should be 20 to approximate a 5us timeout.

Signed-off-by: Tomasz Chudy <Tomasz.Chudy@intel.com>
Signed-off-by: Jacek Danecki <Jacek.Danecki@intel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>