vfio-ccw: Fix a build error due to missing include of linux/slab.h

Include linux/slab.h to fix a build error due to kfree() being undefined.

Fixes: 3f02cb2 ("vfio-ccw: Wire up the CRW irq and CRW region")
Signed-off-by: Sean Christopherson <[email protected]>
Message-Id: <[email protected]>
Signed-off-by: Cornelia Huck <[email protected]>

Author: Sean Christopherson

drivers/s390/cio/vfio_ccw_chp.c

@@ -8,6 +8,7 @@
  *            Eric Farman <[email protected]>
  */
 
+#include <linux/slab.h>
 #include <linux/vfio.h>
 #include "vfio_ccw_private.h"