md: change bitmap_unplug and others to void functions

bitmap_unplug only ever returns 0, so it may as well be void.  Two callers try
to print a message if it returns non-zero, but that message is already printed
by bitmap_file_kick.

write_page returns an error which is not consistently checked.  It always
causes BITMAP_WRITE_ERROR to be set on an error, and that can more
conveniently be checked.

When the return of write_page is checked, an error causes bitmap_file_kick to
be called - so move that call into write_page - and protect against recursive
calls into bitmap_file_kick.

bitmap_update_sb returns an error that is never checked.

So make these 'void' and be consistent about checking the bit.

Signed-off-by: Neil Brown <neilb@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c
index 9eb66c1..a95ada1 100644
--- a/drivers/md/raid10.c
+++ b/drivers/md/raid10.c
@@ -1510,8 +1510,7 @@
 			blk_remove_plug(mddev->queue);
 			spin_unlock_irqrestore(&conf->device_lock, flags);
 			/* flush any pending bitmap writes to disk before proceeding w/ I/O */
-			if (bitmap_unplug(mddev->bitmap) != 0)
-				printk("%s: bitmap file write failed!\n", mdname(mddev));
+			bitmap_unplug(mddev->bitmap);
 
 			while (bio) { /* submit pending writes */
 				struct bio *next = bio->bi_next;