ti: am33xx: fix do_enable_clocks() to accept NULL parameters

Up till this commit passing NULL as input parameter was allowed, but not
handled properly. When a NULL parameter was passed to the function a data
abort was raised.

Signed-off-by: Dario Binacchi <dariobin@libero.it>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/arch/arm/mach-omap2/am33xx/clock.c b/arch/arm/mach-omap2/am33xx/clock.c
index 8819062..130ee6c 100644
--- a/arch/arm/mach-omap2/am33xx/clock.c
+++ b/arch/arm/mach-omap2/am33xx/clock.c
@@ -194,13 +194,14 @@
 	u32 i, max = 100;
 
 	/* Put the clock domains in SW_WKUP mode */
-	for (i = 0; (i < max) && clk_domains[i]; i++) {
+	for (i = 0; (i < max) && clk_domains && clk_domains[i]; i++) {
 		enable_clock_domain(clk_domains[i],
 				    CD_CLKCTRL_CLKTRCTRL_SW_WKUP);
 	}
 
 	/* Clock modules that need to be put in SW_EXPLICIT_EN mode */
-	for (i = 0; (i < max) && clk_modules_explicit_en[i]; i++) {
+	for (i = 0; (i < max) && clk_modules_explicit_en &&
+	     clk_modules_explicit_en[i]; i++) {
 		enable_clock_module(clk_modules_explicit_en[i],
 				    MODULE_CLKCTRL_MODULEMODE_SW_EXPLICIT_EN,
 				    wait_for_enable);
@@ -215,12 +216,13 @@
 
 
 	/* Clock modules that need to be put in SW_DISABLE */
-	for (i = 0; (i < max) && clk_modules_disable[i]; i++)
+	for (i = 0; (i < max) && clk_modules_disable && clk_modules_disable[i];
+	     i++)
 		disable_clock_module(clk_modules_disable[i],
 				     wait_for_disable);
 
 	/* Put the clock domains in SW_SLEEP mode */
-	for (i = 0; (i < max) && clk_domains[i]; i++)
+	for (i = 0; (i < max) && clk_domains && clk_domains[i]; i++)
 		disable_clock_domain(clk_domains[i]);
 }