OMAPDSS: DSI: fix dsi_get_dsidev_from_id()

If dsi_get_dsidev_from_id() is called with a DSI module id that does not
exist on the board, the function will crash as omap_dss_get_output()
will return NULL.

This happens on omap3 boards when dumping DSI clocks, as the dumping
code will try to get the dsidev for DSI modules 0 and 1, but omap3 only
has DSI module 0.

Also clean up the id -> output mapping, so that if the function is
called with invalid module ID it will return NULL.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Cc: Archit Taneja <archit@ti.com>

drivers/video/omap2/dss/dsi.c

@@ -365,11 +365,20 @@ struct platform_device *dsi_get_dsidev_from_id(int module)
 	struct omap_dss_output *out;
 	enum omap_dss_output_id	id;
 
-	id = module == 0 ? OMAP_DSS_OUTPUT_DSI1 : OMAP_DSS_OUTPUT_DSI2;
+	switch (module) {
+	case 0:
+		id = OMAP_DSS_OUTPUT_DSI1;
+		break;
+	case 1:
+		id = OMAP_DSS_OUTPUT_DSI2;
+		break;
+	default:
+		return NULL;
+	}
 
 	out = omap_dss_get_output(id);
 
-	return out->pdev;
+	return out ? out->pdev : NULL;
 }
 
 static inline void dsi_write_reg(struct platform_device *dsidev,