OMAPDSS: Remove manager->device references

With the introduction of output entities, managers will now connect to outputs.
Create helper ops for overlays and managers named get_device. This will abstract
away the information on how to get the device from an overlay or an overlay
manager. The get_device ops currently retrieve the output via a
ovl->manager->device reference. This will be later replaced by
ovl->manager->output->device references.

Signed-off-by: Archit Taneja <archit@ti.com>
diff --git a/drivers/video/omap2/dss/manager-sysfs.c b/drivers/video/omap2/dss/manager-sysfs.c
index 9b875fb..55cf955 100644
--- a/drivers/video/omap2/dss/manager-sysfs.c
+++ b/drivers/video/omap2/dss/manager-sysfs.c
@@ -38,8 +38,10 @@
 
 static ssize_t manager_display_show(struct omap_overlay_manager *mgr, char *buf)
 {
-	return snprintf(buf, PAGE_SIZE, "%s\n",
-			mgr->device ? mgr->device->name : "<none>");
+	struct omap_dss_device *dssdev = mgr->get_device(mgr);
+
+	return snprintf(buf, PAGE_SIZE, "%s\n", dssdev ?
+			dssdev->name : "<none>");
 }
 
 static ssize_t manager_display_store(struct omap_overlay_manager *mgr,
@@ -67,7 +69,7 @@
 	if (dssdev)
 		DSSDBG("display %s found\n", dssdev->name);
 
-	if (mgr->device) {
+	if (mgr->get_device(mgr)) {
 		r = mgr->unset_device(mgr);
 		if (r) {
 			DSSERR("failed to unset display\n");