clk: mxs: Index is always positive

Fix the following warnings when building with W=1 option:

drivers/clk/mxs/clk-imx23.c: In function 'mx23_clocks_init':
drivers/clk/mxs/clk-imx23.c:149:16: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
drivers/clk/mxs/clk-imx23.c:165:16: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
...

drivers/clk/mxs/clk-imx28.c: In function 'mx28_clocks_init':
drivers/clk/mxs/clk-imx28.c:227:16: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
drivers/clk/mxs/clk-imx28.c:244:16: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Acked-by: Shawn Guo <shawn.guo@linaro.org>
Signed-off-by: Mike Turquette <mturquette@linaro.org>

drivers/clk/mxs/clk-imx23.c

@@ -99,7 +99,7 @@ static enum imx23_clk clks_init_on[] __initdata = {
 int __init mx23_clocks_init(void)
 {
 	struct device_node *np;
-	int i;
+	u32 i;
 
 	clk_misc_init();
 

drivers/clk/mxs/clk-imx28.c

@@ -154,7 +154,7 @@ static enum imx28_clk clks_init_on[] __initdata = {
 int __init mx28_clocks_init(void)
 {
 	struct device_node *np;
-	int i;
+	u32 i;
 
 	clk_misc_init();