staging: iio: ad2s1200: Remove unneeded include

This patches removes unneeded slab.h header.
Signed-off-by: David Veenstra <davidjulianveenstra@gmail.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/staging/iio/resolver/ad2s1200.c

@@ -13,7 +13,6 @@
 #include <linux/mutex.h>
 #include <linux/device.h>
 #include <linux/spi/spi.h>
-#include <linux/slab.h>
 #include <linux/sysfs.h>
 #include <linux/delay.h>
 #include <linux/gpio.h>