iio: magnetometer: ak8975: update headers per IWYU principle

Remove kernel.h proxy header and unused headers (slab.h, iio/sysfs.h,
iio/trigger.h). Add missing headers to ensure atomicity (array_size.h,
dev_printk.h, asm/byteorder.h, irqreturn.h, minmax.h, property.h,
types.h, wait.h).

Audited using the include-what-you-use tool.

Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Joshua Crofts <joshua.crofts1@gmail.com>
Reviewed-by: Maxwell Doose <m32285159@gmail.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

Author: cjd8

drivers/iio/magnetometer/ak8975.c

@@ -7,24 +7,29 @@
  * Copyright (c) 2010, NVIDIA Corporation.
  */
 
+#include <linux/array_size.h>
 #include <linux/bitops.h>
 #include <linux/delay.h>
+#include <linux/dev_printk.h>
 #include <linux/err.h>
 #include <linux/gpio/consumer.h>
 #include <linux/i2c.h>
 #include <linux/interrupt.h>
-#include <linux/kernel.h>
+#include <linux/iopoll.h>
+#include <linux/minmax.h>
 #include <linux/mod_devicetable.h>
 #include <linux/module.h>
 #include <linux/mutex.h>
 #include <linux/pm_runtime.h>
+#include <linux/property.h>
 #include <linux/regulator/consumer.h>
-#include <linux/slab.h>
+#include <linux/types.h>
+#include <linux/wait.h>
+
+#include <asm/byteorder.h>
 
 #include <linux/iio/buffer.h>
 #include <linux/iio/iio.h>
-#include <linux/iio/sysfs.h>
-#include <linux/iio/trigger.h>
 #include <linux/iio/trigger_consumer.h>
 #include <linux/iio/triggered_buffer.h>