btrfs: pass a btrfs_inode to btrfs_fdatawrite_range()

Instead of passing a (VFS) inode pointer argument, pass a btrfs_inode
instead, as this is generally what we do for internal APIs, making it
more consistent with most of the code base. This will later allow to
help to remove a lot of BTRFS_I() calls in btrfs_sync_file().

Reviewed-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>