[PATCH] drivers/media/video __user annotations and fixes

* compat_alloc_user_space() returns __user pointer
* copying between two userland areas is copy_in_user(), not copy_from_user()
* dereferencing userland pointers is bad
* so's get_user() from local variables

... plus usual __user annotations

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>