writeback: fix break condition

Commit dcf6a79d ("write-back: fix
nr_to_write counter") fixed nr_to_write counter, but didn't set the break
condition properly.

If nr_to_write == 0 after being decremented it will loop one more time
before setting done = 1 and breaking the loop.

[akpm@linux-foundation.org: coding-style fixes]
Cc: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
Acked-by: Nick Piggin <npiggin@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/page-writeback.c

@@ -1051,21 +1051,24 @@ continue_unlock:
 				}
  			}
 
-			if (nr_to_write > 0)
+			if (nr_to_write > 0) {
 				nr_to_write--;
-			else if (wbc->sync_mode == WB_SYNC_NONE) {
+				if (nr_to_write == 0 &&
+				    wbc->sync_mode == WB_SYNC_NONE) {
 					/*
-				 * We stop writing back only if we are not
-				 * doing integrity sync. In case of integrity
-				 * sync we have to keep going because someone
-				 * may be concurrently dirtying pages, and we
-				 * might have synced a lot of newly appeared
-				 * dirty pages, but have not synced all of the
+					 * We stop writing back only if we are
+					 * not doing integrity sync. In case of
+					 * integrity sync we have to keep going
+					 * because someone may be concurrently
+					 * dirtying pages, and we might have
+					 * synced a lot of newly appeared dirty
+					 * pages, but have not synced all of the
 					 * old dirty pages.
 					 */
 					done = 1;
 					break;
 				}
+			}
 
 			if (wbc->nonblocking && bdi_write_congested(bdi)) {
 				wbc->encountered_congestion = 1;