usb: phy: am335x-control: check return value of bus_find_device

This fixes a potential null pointer dereference.

Cc: <stable@vger.kernel.org> # v3.16+
Fixes: d4332013 ("driver core: dev_get_drvdata: Don't check for NULL dev")
Acked-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: David Dueck <davidcdueck@googlemail.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>

drivers/usb/phy/phy-am335x-control.c

@@ -126,6 +126,9 @@ struct phy_control *am335x_get_phy_control(struct device *dev)
 		return NULL;
 
 	dev = bus_find_device(&platform_bus_type, NULL, node, match);
+	if (!dev)
+		return NULL;
+
 	ctrl_usb = dev_get_drvdata(dev);
 	if (!ctrl_usb)
 		return NULL;