drm/i915/intel_i2c: refactor using intel_gmbus_get_adapter

Instead of letting other modules directly access the ->gmbus array,
introduce intel_gmbus_get_adapter() for looking up an i2c_adapter
for a given gmbus port identifier.  This will enable later refactoring
of the gmbus port list.

Note: Before requesting an adapter for a given gmbus port number, the
driver must first check its validity using i2c_intel_gmbus_is_port_valid().
If this check fails, a call to intel_gmbus_get_adapter() will WARN_ON and
return NULL.  This is relevant for parts of the driver that read a port
from VBIOS, which might be improperly initialized and contain an invalid
port.  In these cases, the driver must fall back to using a safer default
port.

Signed-off-by: Daniel Kurtz <djkurtz@chromium.org>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
diff --git a/drivers/gpu/drm/i915/intel_hdmi.c b/drivers/gpu/drm/i915/intel_hdmi.c
index cae3e5f..1d00f61 100644
--- a/drivers/gpu/drm/i915/intel_hdmi.c
+++ b/drivers/gpu/drm/i915/intel_hdmi.c
@@ -334,7 +334,8 @@
 	intel_hdmi->has_hdmi_sink = false;
 	intel_hdmi->has_audio = false;
 	edid = drm_get_edid(connector,
-			    &dev_priv->gmbus[intel_hdmi->ddc_bus].adapter);
+			    intel_gmbus_get_adapter(dev_priv,
+						    intel_hdmi->ddc_bus));
 
 	if (edid) {
 		if (edid->input & DRM_EDID_INPUT_DIGITAL) {
@@ -367,7 +368,8 @@
 	 */
 
 	return intel_ddc_get_modes(connector,
-				   &dev_priv->gmbus[intel_hdmi->ddc_bus].adapter);
+				   intel_gmbus_get_adapter(dev_priv,
+							   intel_hdmi->ddc_bus));
 }
 
 static bool
@@ -379,7 +381,8 @@
 	bool has_audio = false;
 
 	edid = drm_get_edid(connector,
-			    &dev_priv->gmbus[intel_hdmi->ddc_bus].adapter);
+			    intel_gmbus_get_adapter(dev_priv,
+						    intel_hdmi->ddc_bus));
 	if (edid) {
 		if (edid->input & DRM_EDID_INPUT_DIGITAL)
 			has_audio = drm_detect_monitor_audio(edid);