locking/refcounts: Add missing kernel.h header to have UINT_MAX defined

Fix header dependency.
Suggested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: Elena Reshetova <elena.reshetova@intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1487855374-21993-1-git-send-email-elena.reshetova@intel.comSigned-off-by: Ingo Molnar <mingo@kernel.org>

include/linux/refcount.h

@@ -4,6 +4,7 @@
 #include <linux/atomic.h>
 #include <linux/mutex.h>
 #include <linux/spinlock.h>
+#include <linux/kernel.h>
 
 typedef struct refcount_struct {
 	atomic_t refs;