regulator: da9052: Directly include of.h

Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>

drivers/regulator/da9052-regulator.c

@@ -20,6 +20,7 @@
 #include <linux/regulator/driver.h>
 #include <linux/regulator/machine.h>
 #ifdef CONFIG_OF
+#include <linux/of.h>
 #include <linux/regulator/of_regulator.h>
 #endif