staging: comedi: pcl812: use comedi_legacy_detach()

This driver does not follow the standard (*attach) (*detach) flow of
the other drivers in comedi. Comedi drivers do not 'cleanup' any of
the allocations made during the (*attach) if failures are encountered.
If the (*attach) fails, the comedi core will call the (*detach) to
handle any clenaup.

In this driver, the function free_resources() handles all the cleanup.
Remove the calls to this function during the (*attach). Since the
(*detach) is then the only caller, remove the function and just put
all the cleanup in the (*detach) function.

Use the new comedi_legacy_detach() helper in the (*detach) to release
the I/O region.

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>