f2fs: Convert f2fs_finish_read_bio() to use folios

Use bio_for_each_folio_all() to iterate over each folio in the bio.
This lets us use folio_end_read() which saves an atomic operation and
memory barrier compared to marking the folio uptodate and unlocking
it as two separate operations.  This also removes a few 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>