rcu: Fix nohz status in stall warning

The Documentation/RCU/stallwarn.txt file says that stall warnings
print "D" if dyntick-idle processing is enabled, but the code in
print_cpu_stall_fast_no_hz() prints "." instead.  This commit therefore
reverses the sense of the test to make the code match the documentation.
Signed-off-by: Neeraj Upadhyay <neeraju@codeaurora.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>

kernel/rcu/tree_stall.h

@@ -267,7 +267,7 @@ static void print_cpu_stall_fast_no_hz(char *cp, int cpu)
 		rdp->last_accelerate & 0xffff, jiffies & 0xffff,
 		".l"[rdp->all_lazy],
 		".L"[!rcu_segcblist_n_nonlazy_cbs(&rdp->cblist)],
-		".D"[!rdp->tick_nohz_enabled_snap]);
+		".D"[!!rdp->tick_nohz_enabled_snap]);
 }
 
 #else /* #ifdef CONFIG_RCU_FAST_NO_HZ */