udf: Remove BKL from udf_update_inode

udf_update_inode() does not need BKL since on-disk inode modifications are
protected by the buffer lock and reading of values of in-memory inode is
safe without any lock. In some cases we can write inconsistent inode state
to disk but in that case inode will be marked dirty and overwritten later.

Also make unnecessarily global udf_sync_inode() static.

Signed-off-by: Jan Kara <jack@suse.cz>