f2fs: new helper cur_cp_crc() getting crc in f2fs_checkpoint

There are four places that getting the crc value in f2fs_checkpoint,
just add a new helper cur_cp_crc for them.

Signed-off-by: Kinglong Mee <kinglongmee@gmail.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
index 633f2ef..4d332b3 100644
--- a/fs/f2fs/f2fs.h
+++ b/fs/f2fs/f2fs.h
@@ -1126,6 +1126,12 @@ static inline unsigned long long cur_cp_version(struct f2fs_checkpoint *cp)
 	return le64_to_cpu(cp->checkpoint_ver);
 }
 
+static inline __u64 cur_cp_crc(struct f2fs_checkpoint *cp)
+{
+	size_t crc_offset = le32_to_cpu(cp->checksum_offset);
+	return le32_to_cpu(*((__le32 *)((unsigned char *)cp + crc_offset)));
+}
+
 static inline bool __is_set_ckpt_flags(struct f2fs_checkpoint *cp, unsigned int f)
 {
 	unsigned int ckpt_flags = le32_to_cpu(cp->ckpt_flags);