media: sta2x11: document missing function parameters

As warned:

    drivers/media/pci/sta2x11/sta2x11_vip.c:414: warning: No description found for parameter 'priv'
    drivers/media/pci/sta2x11/sta2x11_vip.c:442: warning: No description found for parameter 'priv'
    drivers/media/pci/sta2x11/sta2x11_vip.c:476: warning: No description found for parameter 'priv'
    drivers/media/pci/sta2x11/sta2x11_vip.c:493: warning: No description found for parameter 'priv'
    drivers/media/pci/sta2x11/sta2x11_vip.c:524: warning: No description found for parameter 'priv'
    drivers/media/pci/sta2x11/sta2x11_vip.c:548: warning: No description found for parameter 'priv'
    drivers/media/pci/sta2x11/sta2x11_vip.c:566: warning: No description found for parameter 'file'
    drivers/media/pci/sta2x11/sta2x11_vip.c:566: warning: No description found for parameter 'priv'
    drivers/media/pci/sta2x11/sta2x11_vip.c:594: warning: No description found for parameter 'priv'
    drivers/media/pci/sta2x11/sta2x11_vip.c:651: warning: No description found for parameter 'priv'
    drivers/media/pci/sta2x11/sta2x11_vip.c:717: warning: No description found for parameter 'priv'

Most of the above are for the unused priv argument.

Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>