[media] vivi: Constify structures

Most of *_ops and other structures in vivi.c were already declared const
but some have not. Constify and code/data will take less space:
    $ size drivers/media/platform/vivi.o
              text    data     bss     dec     hex filename
    before:  12569     248       8   12825    3219 drivers/media/platform/vivi.o
    after:   12308      20       8   12336    3030 drivers/media/platform/vivi.o
i.e. vivi.o is now ~500 bytes less.

Signed-off-by: Kirill Smelkov <kirr@navytux.spb.ru>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>