isci: Cleaning up task execute path.

Made sure the device ready check accounts for all states.
Moved the aborted task check into the loop of pulling task requests
off of the submitted list.

Signed-off-by: Jeff Skirvin <jeffrey.d.skirvin@intel.com>
Signed-off-by: Jacek Danecki <Jacek.Danecki@intel.com>
[remove host and device starting state checks]
Signed-off-by: Dan Williams <dan.j.williams@intel.com>