staging: comedi: mite: rename 'struct mite_struct'

Rename this struct to simply 'mite'. The current name is a bit redundant.

Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Reviewed-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>