USB: gadget: udc: Remove some dead code

The 'drd_wq' workqueue_struct has never been used.
It is only destroyed, but never created.

It was introduced in commit 1b9f35adb0ff ("usb: gadget: udc: Add Synopsys
UDC Platform driver")

Remove the corresponding dead code and save some space from the 'udc'
structure.

Signed-off-by: Christophe JAILLET <[e-mail]>
Link: https://lore.kernel.org/r/9a85b23538[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/usb/gadget/udc/amd5536udc.h

···
 	struct extcon_specific_cable_nb	extcon_nb;
 	struct notifier_block		nb;
 	struct delayed_work		drd_work;
-	struct workqueue_struct		*drd_wq;
 	u32				conn_type;
 };
 

drivers/usb/gadget/udc/snps_udc_plat.c

···
 
 	platform_set_drvdata(pdev, NULL);
 
-	if (dev->drd_wq) {
-		flush_workqueue(dev->drd_wq);
-		destroy_workqueue(dev->drd_wq);
-	}
-
 	phy_power_off(dev->udc_phy);
 	phy_exit(dev->udc_phy);
 	extcon_unregister_notifier(dev->edev, EXTCON_USB, &dev->nb);