Commit fb59581404ab7ec5075299065c22cb211a9262a9 removed
xfs_flushinval_pages() and changed its callers to use
filemap_write_and_wait() and truncate_pagecache_range() directly.
But in xfs_swap_extents() this change accidental switched the argument
for 'tip' to 'ip'. This patch switches it back to 'tip'