clk: hi6220: fix missing clk.h include

Fix the warning from missing "clk.h" include which
defines hi6220_register_clkdiv() function.

drivers/clk/hisilicon/clkdivider-hi6220.c:102:12: warning: symbol 'hi6220_register_clkdiv' was not declared. Should it be static?
Signed-off-by: Ben Dooks <ben.dooks@codethink.co.uk>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>

drivers/clk/hisilicon/clkdivider-hi6220.c

@@ -18,6 +18,8 @@
 #include <linux/err.h>
 #include <linux/spinlock.h>
 
+#include "clk.h"
+
 #define div_mask(width)	((1 << (width)) - 1)
 
 /**