usb: gadget: amd5536udc: remove forward declaration of udc_create_dma_chain

Rearrange udc_create_dma_chain to remove the forward declaration. While
rearranging fixed the relevant checkpatch warnings.

Signed-off-by: Sudip Mukherjee <sudip@vectorindia.org>
Signed-off-by: Felipe Balbi <balbi@ti.com>