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>

arch/arm/plat-omap/clock.c

@@ -101,6 +101,7 @@ void clk_disable(struct clk *clk)
 		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);