media: uvcvideo: Make some structs const

Move some data to text

$ size drivers/media/usb/uvc/uvc_ctrl.o*
   text	   data	    bss	    dec	    hex	filename
  34323	   2364	      0	  36687	   8f4f	drivers/media/usb/uvc/uvc_ctrl.o.new
  28659	   8028	      0	  36687	   8f4f	drivers/media/usb/uvc/uvc_ctrl.o.old

Signed-off-by: Joe Perches <joe@perches.com>
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>