usb: gadget: udc: atmel: fix uninitialized read in debug printk

[ Upstream commit 30517ffe ]

Fixed commit moved the assignment of 'req', but did not update a
reference in the DBG() call. Use the argument as it was renamed.

Fixes: 5fb694f9

 ("usb: gadget: udc: atmel: fix possible oops when unloading module")
Signed-off-by: Michał Mirosław <mirq-linux@rere.qmqm.pl>
Signed-off-by: Felipe Balbi <balbi@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>