f2fs: fix to avoid double unlock

On image that has verity and compression feature, if compressed pages
and non-compressed pages are mixed in one bio, we may double unlock
non-compressed page in below flow:

- f2fs_post_read_work
- f2fs_decompress_work
- f2fs_decompress_bio
- __read_end_io
- unlock_page
- fsverity_enqueue_verify_work
- f2fs_verity_work
- f2fs_verify_bio
- unlock_page

So it should skip handling non-compressed page in f2fs_decompress_work()
if verity is on.

Besides, add missing dec_page_count() in f2fs_verify_bio().

Signed-off-by: Chao Yu <[e-mail]>
Signed-off-by: Jaegeuk Kim <[e-mail]>

fs/f2fs/data.c

···
 			f2fs_decompress_pages(bio, page, verity);
 			continue;
 		}
+		if (verity)
+			continue;
 #endif
 
 		/* PG_error was set if any post_read step failed */
···
 		ClearPageUptodate(page);
 		ClearPageError(page);
 unlock:
+		dec_page_count(F2FS_P_SB(page), __read_io_type(page));
 		unlock_page(page);
 	}
 }