f2fs: Pass a folio to f2fs_cache_compressed_page()

f2fs: Pass a folio to f2fs_cache_compressed_page()

The only caller already has a folio so pass it in.
f2fs_cache_compressed_page() is not used outside compress.c so
make it static.  This requires a forward declaration (or would require
rearranging this file, but I've chosen not to do that for readability of
the diff).

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