libata: don't call ata_scsi_rbuf_fill for command without a response buffer

No need to copy a zeroed buffer to the caller if the command is defined
to not have a response in the SCSI spec.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Tejun Heo <tj@kernel.org>
1 file changed