btrfs: remove constant parameter to memset_extent_buffer and rename it

The only memset we do is to 0, so sink the parameter to the function and
simplify all calls. Rename the function to reflect the behaviour.

Signed-off-by: David Sterba <dsterba@suse.com>
diff --git a/fs/btrfs/ctree.c b/fs/btrfs/ctree.c
index 93bc38b..be362b7 100644
--- a/fs/btrfs/ctree.c
+++ b/fs/btrfs/ctree.c
@@ -3348,7 +3348,7 @@ static noinline int insert_new_root(struct btrfs_trans_handle *trans,
 
 	root_add_used(root, root->nodesize);
 
-	memset_extent_buffer(c, 0, 0, sizeof(struct btrfs_header));
+	memzero_extent_buffer(c, 0, sizeof(struct btrfs_header));
 	btrfs_set_header_nritems(c, 1);
 	btrfs_set_header_level(c, level);
 	btrfs_set_header_bytenr(c, c->start);
@@ -3484,7 +3484,7 @@ static noinline int split_node(struct btrfs_trans_handle *trans,
 
 	root_add_used(root, root->nodesize);
 
-	memset_extent_buffer(split, 0, 0, sizeof(struct btrfs_header));
+	memzero_extent_buffer(split, 0, sizeof(struct btrfs_header));
 	btrfs_set_header_level(split, btrfs_header_level(c));
 	btrfs_set_header_bytenr(split, split->start);
 	btrfs_set_header_generation(split, trans->transid);
@@ -4270,7 +4270,7 @@ static noinline int split_leaf(struct btrfs_trans_handle *trans,
 
 	root_add_used(root, root->nodesize);
 
-	memset_extent_buffer(right, 0, 0, sizeof(struct btrfs_header));
+	memzero_extent_buffer(right, 0, sizeof(struct btrfs_header));
 	btrfs_set_header_bytenr(right, right->start);
 	btrfs_set_header_generation(right, trans->transid);
 	btrfs_set_header_backref_rev(right, BTRFS_MIXED_BACKREF_REV);