sata_mv: safer logic for limit_warnings

There is a miniscule chance that two separate host controllers
might be in sata_mv at the same time and manage to decrement
the static limit_warnings variable below zero.

Fix the comparison to deal with it.

Signed-off-by: Mark Lord <mlord@pobox.com>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>

drivers/ata/sata_mv.c

@@ -1607,7 +1607,7 @@ static unsigned int mv_qc_issue(struct ata_queued_cmd *qc)
 		 * Much of the time, this could just work regardless.
 		 * So for now, just log the incident, and allow the attempt.
 		 */
-		if (limit_warnings && (qc->nbytes / qc->sect_size) > 1) {
+		if (limit_warnings > 0 && (qc->nbytes / qc->sect_size) > 1) {
 			--limit_warnings;
 			ata_link_printk(qc->dev->link, KERN_WARNING, DRV_NAME
 					": attempting PIO w/multiple DRQ: "