OMAP2PLUS: DSS2: Cleanup clock source related code

Clean up some of the DSS functions which select/get clock sources, use switch
to select the clock source members since more clock sources will be introduced
later on.

Remove the use of macro CONFIG_OMAP2_DSS_DSI in dispc_fclk_rate, use a dummy
inline for function for dsi_get_pll_hsdiv_dispc_rate() instead for code clarity.

Signed-off-by: Archit Taneja <archit@ti.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
diff --git a/drivers/video/omap2/dss/dss.h b/drivers/video/omap2/dss/dss.h
index 85d4141..fc41b3f 100644
--- a/drivers/video/omap2/dss/dss.h
+++ b/drivers/video/omap2/dss/dss.h
@@ -299,6 +299,11 @@
 static inline void dsi_uninit_platform_driver(void)
 {
 }
+static inline unsigned long dsi_get_pll_hsdiv_dispc_rate(void)
+{
+	WARN("%s: DSI not compiled in, returning rate as 0\n", __func__);
+	return 0;
+}
 static inline void dsi_wait_pll_hsdiv_dispc_active(void)
 {
 }