mfd: wm8350-core: Don't use "proxy" headers

Update header inclusions to follow IWYU (Include What You Use)
principle.

Note that kernel.h is discouraged to be included as it's written
at the top of that file.

Signed-off-by: Andy Shevchenko <[e-mail]>
Reviewed-by: Charles Keepax <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Lee Jones <[e-mail]>

include/linux/mfd/wm8350/core.h

···
 #ifndef __LINUX_MFD_WM8350_CORE_H_
 #define __LINUX_MFD_WM8350_CORE_H_
 
-#include <linux/kernel.h>
-#include <linux/mutex.h>
-#include <linux/interrupt.h>
 #include <linux/completion.h>
+#include <linux/errno.h>
+#include <linux/interrupt.h>
+#include <linux/mutex.h>
 #include <linux/regmap.h>
+#include <linux/types.h>
 
 #include <linux/mfd/wm8350/audio.h>
 #include <linux/mfd/wm8350/gpio.h>
···
 #include <linux/mfd/wm8350/rtc.h>
 #include <linux/mfd/wm8350/supply.h>
 #include <linux/mfd/wm8350/wdt.h>
+
+struct device;
+struct platform_device;
 
 /*
  * Register values.