usb: gadget: udc: atmel: Make some symbols static

Fix the following sparse warnings:

drivers/usb/gadget/udc/atmel_usba_udc.c:188:30: warning: symbol 'queue_dbg_fops' was not declared.
drivers/usb/gadget/udc/atmel_usba_udc.c:196:30: warning: symbol 'regs_dbg_fops' was not declared.

queue_dbg_fops and regs_dbg_fops have only call within atmel_usba_udc.c
They should be static

Fixes: 914a3f3b

 ("USB: add atmel_usba_udc driver")
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Samuel Zou <zou_wei@huawei.com>
Signed-off-by: Felipe Balbi <balbi@kernel.org>