mailbox: remove unnecessary platform_set_drvdata()

The driver core clears the driver data to NULL after device_release
or on probe failure. Thus, it is not needed to manually clear the
device driver data to NULL.
Signed-off-by: Jingoo Han <jg1.han@samsung.com>
Acked-by: Suman Anna <s-anna@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>

drivers/mailbox/mailbox-omap2.c

@@ -325,7 +325,6 @@ static int omap2_mbox_remove(struct platform_device *pdev)
 	kfree(privblk);
 	kfree(mboxblk);
 	kfree(list);
-	platform_set_drvdata(pdev, NULL);
 
 	return 0;
 }