usb: ehci-exynos: Use NULL instead of 0

The third argument of devm_of_phy_get expects a pointer.
Hence use NULL instead of 0. Fixes the following warning:
drivers/usb/host/ehci-exynos.c:91:51: warning: Using plain integer as NULL pointer

Signed-off-by: Sachin Kamat <sachin.kamat@samsung.com>
Acked-by: Jingoo Han <jg1.han@samsung.com>
Reviewed-by: Vivek Gautam <gautam.vivek@samsung.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/host/ehci-exynos.c

@@ -88,7 +88,7 @@ static int exynos_ehci_get_phy(struct device *dev,
 			return -EINVAL;
 		}
 
-		phy = devm_of_phy_get(dev, child, 0);
+		phy = devm_of_phy_get(dev, child, NULL);
 		of_node_put(child);
 		if (IS_ERR(phy)) {
 			ret = PTR_ERR(phy);