aio: Configuration issue in aio driver

The reference and polarity fields of the config struct which is passed
to qm_set_config are never cleared, meaning the wrong configuration
may be written if aio_set_config is called for different sets of pins
in the same program.

This patch clears these fields in aio_cmp_disable to prevent such an
issue.

Change-Id: I8feabae1f3d9fa4c7260d94c1ec919ef2fb84bfb
Signed-off-by: James Fagan <james.p.fagan@intel.com>