usb: gadget: udc: Provide correct arguments for 'dma_pool_create'

Change the argument from NULL to a struct device for the
dma_pool_create call during dma init.

Signed-off-by: Raviteja Garimella <raviteja.garimella@broadcom.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>