libata: Fixup n_elem initialization

Fixup the inialization of qc->n_elem. It currently gets
initialized to 1 for commands that do not transfer any data.
Fix this by initializing n_elem to 0 and only setting to 1
in ata_scsi_qc_new when there is data to transfer. This fixes
some problems seen with SATA devices attached to ipr adapters.
Signed-off-by: Brian King <brking@linux.vnet.ibm.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>

drivers/ata/libata-scsi.c

@@ -372,7 +372,7 @@ struct ata_queued_cmd *ata_scsi_qc_new(struct ata_device *dev,
 		if (cmd->use_sg) {
 			qc->__sg = (struct scatterlist *) cmd->request_buffer;
 			qc->n_elem = cmd->use_sg;
-		} else {
+		} else if (cmd->request_bufflen) {
 			qc->__sg = &qc->sgent;
 			qc->n_elem = 1;
 		}

include/linux/libata.h

@@ -1149,6 +1149,7 @@ static inline void ata_qc_reinit(struct ata_queued_cmd *qc)
 	qc->cursect = qc->cursg = qc->cursg_ofs = 0;
 	qc->nsect = 0;
 	qc->nbytes = qc->curbytes = 0;
+	qc->n_elem = 0;
 	qc->err_mask = 0;
 
 	ata_tf_init(qc->dev, &qc->tf);