staging: comedi: do not return -ENOSYS.

fixed coding style issue by replacing ENOSYS
with EIO because it means 'invalid syscall nr'
and nothing else.

Signed-off-by: Ted Chen <tedc.37zngo@gmail.com>
Reviewed-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>