usb: gadget: amd5536udc: remove forward declaration of udc_free_dma_chain

Rearrange udc_free_dma_chain to remove the forward declaration. While at
it fixed all the relevant checkpatch warnings.

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