ARM: OMAP: Add sanity check to clk_disable

BUG() if the clock use count is already zero.

Signed-off-by: Juha Yrjola <juha.yrjola@solidboot.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>
diff --git a/arch/arm/plat-omap/clock.c b/arch/arm/plat-omap/clock.c
index 7f45c7c..4abf271 100644
--- a/arch/arm/plat-omap/clock.c
+++ b/arch/arm/plat-omap/clock.c
@@ -100,6 +100,7 @@
 		return;
 
 	spin_lock_irqsave(&clockfw_lock, flags);
+	BUG_ON(clk->usecount == 0);
 	if (arch_clock->clk_disable)
 		arch_clock->clk_disable(clk);
 	spin_unlock_irqrestore(&clockfw_lock, flags);