x86: UV fix uv_flush_send_and_wait()

Impact: fix possible tlb mis-flushing on UV

uv_flush_send_and_wait() should return a pointer if the broadcast
remote tlb shootdown requests fail. That causes the conventional IPI
method of shootdown to be used.
Signed-off-by: NCliff Wickman <cpw@sgi.com>
Signed-off-by: NTejun Heo <tj@kernel.org>

arch/x86/kernel/tlb_uv.c

@@ -259,7 +259,7 @@ const struct cpumask *uv_flush_send_and_wait(int cpu, int this_blade,
 		 * the cpu's, all of which are still in the mask.
 		 */
 		__get_cpu_var(ptcstats).ptc_i++;
-		return 0;
+		return flush_mask;
 	}
 
 	/*