tools/kernel.h: Replace synchronize_sched() with synchronize_rcu()

Now that synchronize_rcu() waits for preempt-disable regions of code
as well as RCU read-side critical sections, synchronize_sched() can be
replaced by synchronize_rcu().  This commit therefore makes this change,
even though it is but a comment.

Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: <linux-kernel@vger.kernel.org>

tools/include/linux/kernel.h

@@ -116,6 +116,6 @@ int scnprintf(char * buf, size_t size, const char * fmt, ...);
 #define round_down(x, y) ((x) & ~__round_mask(x, y))
 
 #define current_gfp_context(k) 0
-#define synchronize_sched()
+#define synchronize_rcu()
 
 #endif