staging: comedi: mite.h: needs <linux/slab.h>

As reported by the kbuild test robot:

Commit: 0bdab509
staging: comedi: usee comedi_alloc_devpriv

Removed the include of <linux/slab.h> from many of the comedi drivers.
Unfortunately, this header uses kfree() in an inline function.

Instead of adding <linux/slab.h> to each of the drivers that use this
header, include slab.h here.
Signed-off-by: NH Hartley Sweeten <hsweeten@visionengravers.com>
Reported-by: Nkbuild test robot <fengguang.wu@intel.com>
Cc: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/comedi/drivers/mite.h

@@ -21,6 +21,7 @@
 
 #include <linux/pci.h>
 #include <linux/log2.h>
+#include <linux/slab.h>
 #include "../comedidev.h"
 
 /*  #define DEBUG_MITE */