OMAPDSS: DISPC: fix sparse warning

Fix sparse warning:

drivers/video/omap2/dss/dispc.c:3320:6: warning: symbol
'dispc_dump_irqs' was not declared. Should it be static?
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Reported-by: Fengguang Wu <fengguang.wu@intel.com>

drivers/video/omap2/dss/dispc.c

@@ -3317,7 +3317,7 @@ void dispc_dump_clocks(struct seq_file *s)
 }
 
 #ifdef CONFIG_OMAP2_DSS_COLLECT_IRQ_STATS
-void dispc_dump_irqs(struct seq_file *s)
+static void dispc_dump_irqs(struct seq_file *s)
 {
 	unsigned long flags;
 	struct dispc_irq_stats stats;