drm/radeon/dp: return -EIO for flags not zero case

commit f6be5e64 upstream.

If there are error flags in the aux transaction return
-EIO rather than -EBUSY.  -EIO restarts the whole transaction
while -EBUSY jus retries.  Fixes problematic aux transfers.

Bug:
https://bugs.freedesktop.org/show_bug.cgi?id=80684Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
[bwh: Backported to 3.2: error code is returned directly here]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

drivers/gpu/drm/radeon/atombios_dp.c

@@ -89,7 +89,7 @@ static int radeon_process_aux_ch(struct radeon_i2c_chan *chan,
 	/* flags not zero */
 	if (args.v1.ucReplyStatus == 2) {
 		DRM_DEBUG_KMS("dp_aux_ch flags not zero\n");
-		return -EBUSY;
+		return -EIO;
 	}
 
 	/* error */