ARM: OMAP 2: Camera: Fix device release

If streaming wasn't stopped before a file handle was closed,
videobuf_streamoff got called after cam->streaming had been set NULL,
causing an oops. Call videobuf_streamoff a bit earlier instead.

Signed-off-by: Sakari Ailus <sakari.ailus@nokia.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>