Fix the following sparse warning:

drivers/usb/cdns3/gadget.c:85:6: warning: symbol
'cdns3_clear_register_bit' was not declared. Should it be static?
drivers/usb/cdns3/gadget.c:140:26: warning: symbol
'cdns3_next_align_buf' was not declared. Should it be static?
drivers/usb/cdns3/gadget.c:151:22: warning: symbol
'cdns3_next_priv_request' was not declared. Should it be static?
drivers/usb/cdns3/gadget.c:193:5: warning: symbol 'cdns3_ring_size' was
not declared. Should it be static?
drivers/usb/cdns3/gadget.c:348:6: warning: symbol
'cdns3_move_deq_to_next_trb' was not declared. Should it be static?
drivers/usb/cdns3/gadget.c:514:20: warning: symbol
'cdns3_wa2_gadget_giveback' was not declared. Should it be static?
drivers/usb/cdns3/gadget.c:554:5: warning: symbol
'cdns3_wa2_gadget_ep_queue' was not declared. Should it be static?
drivers/usb/cdns3/gadget.c:839:6: warning: symbol
'cdns3_wa1_restore_cycle_bit' was not declared. Should it be static?
drivers/usb/cdns3/gadget.c:1907:6: warning: symbol
'cdns3_stream_ep_reconfig' was not declared. Should it be static?
drivers/usb/cdns3/gadget.c:1928:6: warning: symbol
'cdns3_configure_dmult' was not declared. Should it be static?
Reported-by: Hulk Robot <hulkci@huawei.com>
Reviewed-by: Peter Chen <peter.chen@nxp.com>
Signed-off-by: Jason Yan <yanaijie@huawei.com>
Signed-off-by: Felipe Balbi <balbi@kernel.org>