usb: musb: ux500: Fix NULL pointer dereference at system PM

The commit 7d32cdef5356 ("usb: musb: fail with error when no DMA
controller set"), caused the core platform driver to correctly return an
error code when fail probing.

Unfurtante it also caused bug for a NULL pointer dereference, during
system suspend for the ux500 driver. The reason is a lacking validation
of the corresponding ->driver_data pointer, which won't be set when the
musb core driver fails to probe (or haven't yet been probed).

Fixes: 7d32cdef5356 ("usb: musb: fail with error when no DMA...")
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Signed-off-by: Felipe Balbi <balbi@kernel.org>

drivers/usb/musb/ux500.c

@@ -348,7 +348,9 @@ static int ux500_suspend(struct device *dev)
 	struct ux500_glue	*glue = dev_get_drvdata(dev);
 	struct musb		*musb = glue_to_musb(glue);
 
-	usb_phy_set_suspend(musb->xceiv, 1);
+	if (musb)
+		usb_phy_set_suspend(musb->xceiv, 1);
+
 	clk_disable_unprepare(glue->clk);
 
 	return 0;
@@ -366,7 +368,8 @@ static int ux500_resume(struct device *dev)
 		return ret;
 	}
 
-	usb_phy_set_suspend(musb->xceiv, 0);
+	if (musb)
+		usb_phy_set_suspend(musb->xceiv, 0);
 
 	return 0;
 }