sun4M: add include of slab.h for kzalloc

This was being included implicitly via cgroup.h's inclusion of xattr.h
(which has now been removed).
Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>
Acked-by: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: Tejun Heo <tj@kernel.org>

arch/sparc/kernel/sun4m_irq.c

@@ -9,6 +9,8 @@
  *  Copyright (C) 1996 Dave Redman (djhr@tadpole.co.uk)
  */
 
+#include <linux/slab.h>
+
 #include <asm/timer.h>
 #include <asm/traps.h>
 #include <asm/pgalloc.h>