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 1b9f35ad ("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 <christophe.jaillet@wanadoo.fr>
Link: https://lore.kernel.org/r/9a85b2353843b95e2d86acb3103967fd405a8536.1633865503.git.christophe.jaillet@wanadoo.fr


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>