drm/omap: remove read_irqenable()

We only use read_irqenable() to flush posted write. Instead of having a
separate function for this, do the flush implicitly in write_irqenable().
Thus we can remove read_irqenable().

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

drivers/gpu/drm/omapdrm/dss/omapdss.h

@@ -880,7 +880,6 @@ void dss_mgr_unregister_framedone_handler(enum omap_channel channel,
 struct dispc_ops {
 	u32 (*read_irqstatus)(void);
 	void (*clear_irqstatus)(u32 mask);
-	u32 (*read_irqenable)(void);
 	void (*write_irqenable)(u32 mask);
 
 	int (*request_irq)(irq_handler_t handler, void *dev_id);