libata-eh: update atapi_eh_request_sense() to take @dev instead of @qc

Update atapi_eh_request_sense() to take @dev, @sense_buf and
@dfl_sense_key instead of taking @qc and extracting information from
it.  This change is to make the function more generic and allow it to
be called from other places.

While at it, make cdb initialization use initializer.

Signed-off-by: Tejun Heo <htejun@gmail.com>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>