staging: comedi: dt9812: factor the endpoint setup out of dt9812_probe()

When this driver is converted to the comedi (*auto_attach) mechanism the
endpoint setup will be done during the (*auto_attach). To make the
conversion cleaner, factor the endpoint setup out of the (*probe).

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