Check send_sync_cdb return value in sop_sg_io
Delete some unnecessary code

Code was previously copied elsewhere, but not deleted from original location.
prevent unintended sign extension
Remove unnecessary check if h is null in sop_remove().

h cannot be null there since we already dereferenced it a few
lines earlier.  And if it *is* null in sop_remove, there's nothing
sane we can do.  And Coverity complains about null checks after
dereference.
fix comparison of unsigned value to less than zero in sop_delete_io_queue