f2fs: Add f2fs_get_lock_data_folio()

Convert f2fs_get_lock_data_page() to f2fs_get_lock_data_folio() and
add a compatibility wrapper.  Removes three hidden calls to
compound_head().

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>