clk/ux500: explicitly include register header

The ux500 clock driver file named u8500_clk.c does not compile
if it loose implicit dependencies to <mach/db8500-regs.h>
(I have no clue what files will include this) which manifests
itself as I'm experimenting with SPARSE_IRQ so make the
dependency explicit.

Cc: Mike Turquette <mturquette@linaro.org>
Acked-by: Ulf Hansson <ulf.hansson@linaro.org>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

drivers/clk/ux500/u8500_clk.c

@@ -12,7 +12,7 @@
 #include <linux/clk-provider.h>
 #include <linux/mfd/dbx500-prcmu.h>
 #include <linux/platform_data/clk-ux500.h>
-
+#include <mach/db8500-regs.h>
 #include "clk.h"
 
 void u8500_clk_init(void)