Remove error return from check graph driver func

Signed-off-by: Michael Crosby <crosbymichael@gmail.com>

daemon/graphdriver/driver.go

@@ -145,19 +145,16 @@ func New(root string, options []string) (driver Driver, err error) {
 	return nil, fmt.Errorf("No supported storage backend found")
 }
 
-func checkPriorDriver(name string, root string) error {
-
-	var priorDrivers []string
-
+func checkPriorDriver(name, root string) {
+	priorDrivers := []string{}
 	for prior := range drivers {
-		if _, err := os.Stat(path.Join(root, prior)); err == nil && prior != name {
-			priorDrivers = append(priorDrivers, prior)
+		if prior != name {
+			if _, err := os.Stat(path.Join(root, prior)); err == nil {
+				priorDrivers = append(priorDrivers, prior)
+			}
 		}
 	}
-
 	if len(priorDrivers) > 0 {
 		log.Warnf("graphdriver %s selected. Warning: your graphdriver directory %s already contains data managed by other graphdrivers: %s", name, root, strings.Join(priorDrivers, ","))
 	}
-
-	return nil
 }