scsi_debug: make dump_sector static

fixes warning:
warning: no previous prototype for ‘dump_sector’
Signed-off-by: Tomas Winkler <tomas.winkler@intel.com>
Acked-by: Douglas Gilbert <dgilbert@interlog.com>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: James Bottomley <JBottomley@Odin.com>

drivers/scsi/scsi_debug.c

@@ -2681,7 +2681,7 @@ resp_read_dt0(struct scsi_cmnd *scp, struct sdebug_dev_info *devip)
 	return 0;
 }
 
-void dump_sector(unsigned char *buf, int len)
+static void dump_sector(unsigned char *buf, int len)
 {
 	int i, j, n;