btrfs: use nodesize everywhere, kill leafsize

The nodesize and leafsize were never of different values. Unify the
usage and make nodesize the one. Cleanup the redundant checks and
helpers.

Shaves a few bytes from .text:

  text    data     bss     dec     hex filename
852418   24560   23112  900090   dbbfa btrfs.ko.before
851074   24584   23112  898770   db6d2 btrfs.ko.after

Signed-off-by: David Sterba <dsterba@suse.cz>
Signed-off-by: Chris Mason <clm@fb.com>
diff --git a/fs/btrfs/qgroup.c b/fs/btrfs/qgroup.c
index ded5c60..2ce4ce7 100644
--- a/fs/btrfs/qgroup.c
+++ b/fs/btrfs/qgroup.c
@@ -2237,7 +2237,6 @@
 	if (srcid) {
 		struct btrfs_root *srcroot;
 		struct btrfs_key srckey;
-		int srcroot_level;
 
 		srckey.objectid = srcid;
 		srckey.type = BTRFS_ROOT_ITEM_KEY;
@@ -2249,8 +2248,7 @@
 		}
 
 		rcu_read_lock();
-		srcroot_level = btrfs_header_level(srcroot->node);
-		level_size = btrfs_level_size(srcroot, srcroot_level);
+		level_size = srcroot->nodesize;
 		rcu_read_unlock();
 	}
 
@@ -2566,7 +2564,7 @@
 		    found.type != BTRFS_METADATA_ITEM_KEY)
 			continue;
 		if (found.type == BTRFS_METADATA_ITEM_KEY)
-			num_bytes = fs_info->extent_root->leafsize;
+			num_bytes = fs_info->extent_root->nodesize;
 		else
 			num_bytes = found.offset;