drm/i915/lspcon: Get DDC adapter via container_of() instead of cached ptr

We can use the container_of() magic to get to the DDC adapter, so no
need for caching a pointer to it. We'll also need to get at the intel_dp
ptr in the following patch, so add a helper that can be used for both
purposes.

Cc: Shashank Sharma <[e-mail]>
Signed-off-by: Imre Deak <[e-mail]>
Reviewed-by: Jani Nikula <[e-mail]>
Link: http://patchwork.freedesktop.org/patch/msgid/[e-mail]

drivers/gpu/drm/i915/intel_drv.h

···
 struct intel_lspcon {
 	bool active;
 	enum drm_lspcon_mode mode;
-	struct drm_dp_aux *aux;
 };
 
 struct intel_digital_port {

drivers/gpu/drm/i915/intel_lspcon.c

···
 #include <drm/drm_dp_dual_mode_helper.h>
 #include "intel_drv.h"
 
+static struct intel_dp *lspcon_to_intel_dp(struct intel_lspcon *lspcon)
+{
+	struct intel_digital_port *dig_port =
+		container_of(lspcon, struct intel_digital_port, lspcon);
+
+	return &dig_port->dp;
+}
+
 static enum drm_lspcon_mode lspcon_get_current_mode(struct intel_lspcon *lspcon)
 {
 	enum drm_lspcon_mode current_mode = DRM_LSPCON_MODE_INVALID;
-	struct i2c_adapter *adapter = &lspcon->aux->ddc;
+	struct i2c_adapter *adapter = &lspcon_to_intel_dp(lspcon)->aux.ddc;
 
 	if (drm_lspcon_get_mode(adapter, &current_mode))
 		DRM_ERROR("Error reading LSPCON mode\n");
···
 {
 	int err;
 	enum drm_lspcon_mode current_mode;
-	struct i2c_adapter *adapter = &lspcon->aux->ddc;
+	struct i2c_adapter *adapter = &lspcon_to_intel_dp(lspcon)->aux.ddc;
 
 	err = drm_lspcon_get_mode(adapter, &current_mode);
 	if (err) {
···
 static bool lspcon_probe(struct intel_lspcon *lspcon)
 {
 	enum drm_dp_dual_mode_type adaptor_type;
-	struct i2c_adapter *adapter = &lspcon->aux->ddc;
+	struct i2c_adapter *adapter = &lspcon_to_intel_dp(lspcon)->aux.ddc;
 
 	/* Lets probe the adaptor and check its type */
 	adaptor_type = drm_dp_dual_mode_detect(adapter);
···
 
 	lspcon->active = false;
 	lspcon->mode = DRM_LSPCON_MODE_INVALID;
-	lspcon->aux = &dp->aux;
 
 	if (!lspcon_probe(lspcon)) {
 		DRM_ERROR("Failed to probe lspcon\n");