clk: shmobile: fix sparse NULL pointer warning

Fixes the following sparse warnings:

drivers/clk/shmobile/clk-sh73a0.c:57:17: warning:
 Using plain integer as NULL pointer
Signed-off-by: NWei Yongjun <yongjun_wei@trendmicro.com.cn>
Signed-off-by: NSimon Horman <horms+renesas@verge.net.au>

drivers/clk/shmobile/clk-sh73a0.c

@@ -54,7 +54,7 @@ static struct div4_clk div4_clks[] = {
 	{ "m2", "pll1", CPG_FRQCRA,  0 },
 	{ "zx", "pll1", CPG_FRQCRB, 12 },
 	{ "hp", "pll1", CPG_FRQCRB,  4 },
-	{ NULL, 0, 0, 0 },
+	{ NULL, NULL, 0, 0 },
 };
 
 static const struct clk_div_table div4_div_table[] = {