staging: vboxvideo: Do not return -ENOSYS

New instances of ENOSYS are errors. ENOSYS should be used for nonexistent
syscalls only. Use ENODEV instead as there should not be any other
driver for a virtual device that might share buffers with vboxvideo.

In vbox_prime.c, replace all occurrences of -ENOSYS with -ENODEV to fix
checkpatch.pl warning:

WARNING: ENOSYS means 'invalid syscall nr' and nothing else

Signed-off-by: Debleena Sen <idebleenasen@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>