auxdisplay: max6959: Replace slab.h with device/devres.h

Replace slab.h with device/devres.h as the devm_*() APIs are defined
in the latter.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>

drivers/auxdisplay/max6959.c

@@ -11,13 +11,13 @@
 #include <linux/bitrev.h>
 #include <linux/bits.h>
 #include <linux/container_of.h>
+#include <linux/device/devres.h>
 #include <linux/err.h>
 #include <linux/i2c.h>
 #include <linux/mod_devicetable.h>
 #include <linux/module.h>
 #include <linux/pm.h>
 #include <linux/regmap.h>
-#include <linux/slab.h>
 #include <linux/types.h>
 #include <linux/workqueue.h>