staging: comedi: call comedi_release_hardware_device() on error

If `comedi_auto_config()` fails after allocating the minor device, call
`comedi_release_hardware_device()` instead of
`comedi_free_board_minor()` to free the minor device.  That's the same
call that `comedi_auto_unconfig()` uses, and is slightly safer as it
checks the minor device number is still tied to the same hardware
device.

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>