ata: fix sparse warning in libata-core.c

rc is used to test the return value and possibly return an error.
No need to redeclare inside the loop.

drivers/ata/libata-core.c:7089:7: warning: symbol 'rc' shadows an earlier one
drivers/ata/libata-core.c:7030:9: originally declared here
Signed-off-by: NHarvey Harrison <harvey.harrison@gmail.com>
Signed-off-by: NJeff Garzik <jeff@garzik.org>

drivers/ata/libata-core.c

@@ -7086,7 +7086,6 @@ int ata_host_register(struct ata_host *host, struct scsi_host_template *sht)
 	DPRINTK("probe begin\n");
 	for (i = 0; i < host->n_ports; i++) {
 		struct ata_port *ap = host->ports[i];
-		int rc;
 
 		/* probe */
 		if (ap->ops->error_handler) {