usb: gadget: constify all struct usb_gadget_ops

Add the missing 'const' keyword to all struct
usb_gadget_ops in the gadget framework.

Signed-off-by: Felipe Balbi <balbi@ti.com>

diff --cc drivers/usb/gadget/fsl_qe_udc.c
Simple merge

diff --cc drivers/usb/gadget/fsl_udc_core.c
Simple merge

diff --cc drivers/usb/gadget/fusb300_udc.c
Simple merge

diff --cc drivers/usb/gadget/m66592-udc.c
Simple merge

diff --cc drivers/usb/gadget/omap_udc.c
Simple merge

diff --cc drivers/usb/gadget/r8a66597-udc.c
Simple merge

diff --cc drivers/usb/gadget/s3c-hsotg.c
Simple merge

diff --cc drivers/usb/gadget/s3c-hsudc.c
Simple merge

diff --cc drivers/usb/renesas_usbhs/mod_gadget.c
Simple merge