msm: clock-debug: Fix NULL pointer in clock_debug_print_enabled()

The is_enabled() clock op is optional. Check to make sure it's not
NULL before calling it.

Signed-off-by: Matt Wagantall <mattw@codeaurora.org>
diff --git a/arch/arm/mach-msm/clock-debug.c b/arch/arm/mach-msm/clock-debug.c
index d1b9ad0..c0af9b5 100644
--- a/arch/arm/mach-msm/clock-debug.c
+++ b/arch/arm/mach-msm/clock-debug.c
@@ -154,7 +154,7 @@
 	for (i = 0; i < num_msm_clocks; i++) {
 		clk = msm_clocks[i].clk;
 
-		if (clk && clk->ops->is_enabled(clk)) {
+		if (clk && clk->ops->is_enabled && clk->ops->is_enabled(clk)) {
 			pr_info("\t%s\n", clk->dbg_name);
 			cnt++;
 		}