usb: gadget: amd5536udc: remove forward declaration of udc_probe

Rearrange the udc_probe function to remove the forward declarations.
While rearranging also fixed the relevant checkpatch warnings.

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