staging: comedi: remove comedi_clear_minor()

`comedi_clear_minor()` calls either `comedi_clear_board_minor()` or
`comedi_clear_subdevice_minor()` depending on its minor device number
parameter.  The one it calls only depends on where it is called from, so
bypass the calls to `comedi_clear_minor()` and remove it.

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