btrfs: convert correctness BUG_ON()'s to ASSERT()'s in walk_up_proc()

In walk_up_proc() we have several sanity checks that should only trip if
the programmer made a mistake.  Convert these to ASSERT()'s instead of
BUG_ON()'s.
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/extent-tree.c

@@ -5747,7 +5747,7 @@ static noinline int walk_up_proc(struct btrfs_trans_handle *trans,
 	u64 parent = 0;
 
 	if (wc->stage == UPDATE_BACKREF) {
-		BUG_ON(wc->shared_level < level);
+		ASSERT(wc->shared_level >= level);
 		if (level < wc->shared_level)
 			goto out;
 
@@ -5765,7 +5765,7 @@ static noinline int walk_up_proc(struct btrfs_trans_handle *trans,
 		 * count is one.
 		 */
 		if (!path->locks[level]) {
-			BUG_ON(level == 0);
+			ASSERT(level > 0);
 			btrfs_tree_lock(eb);
 			path->locks[level] = BTRFS_WRITE_LOCK;
 
@@ -5794,7 +5794,7 @@ static noinline int walk_up_proc(struct btrfs_trans_handle *trans,
 	}
 
 	/* wc->stage == DROP_REFERENCE */
-	BUG_ON(wc->refs[level] > 1 && !path->locks[level]);
+	ASSERT(path->locks[level] || wc->refs[level] == 1);
 
 	if (wc->refs[level] == 1) {
 		if (level == 0) {