regmap: Fix implicit inclusion of device.h

internal.h is using dev_name() but doesn't include device.h which
defines it.  Add an explicit include to avoid build problems due to
this.

Tested-by: Alexander Stein <alexander.stein@systec-electronic.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

drivers/base/regmap/internal.h

@@ -13,6 +13,7 @@
 #ifndef _REGMAP_INTERNAL_H
 #define _REGMAP_INTERNAL_H
 
+#include <linux/device.h>
 #include <linux/regmap.h>
 #include <linux/fs.h>
 #include <linux/list.h>