CHROMIUM: drm/anx7808: anx7808 disconnect handling

CHROMIUM: drm/anx7808: anx7808 disconnect handling

Currently, if the analogix dongle is disconnected during setup, the setup
function will get stuck.  Handle this by checking for polling error even during
connection process.

BUG=chrome-os-partner:19436
TEST=Plug in a MyDP dongle without connecting to any monitor, then disconnect.
Following that, plug in with connection to monitor.  See that connection is
established.

Change-Id: Ib531547b744d9bd8d07b933448fefc7af6158c4e
Signed-off-by: Jeremy Thorpe <jeremyt@chromium.org>
Reviewed-on: https://gerrit.chromium.org/gerrit/51301
Reviewed-by: Stéphane Marchesin <marcheu@chromium.org>