f2fs: recycle unused compress_data.chksum feild

In Struct compress_data, chksum field was never used, remove it.
Signed-off-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/compress.c

@@ -380,7 +380,6 @@ static int f2fs_compress_pages(struct compress_ctx *cc)
 	}
 
 	cc->cbuf->clen = cpu_to_le32(cc->clen);
-	cc->cbuf->chksum = cpu_to_le32(0);
 
 	for (i = 0; i < COMPRESS_DATA_RESERVED_SIZE; i++)
 		cc->cbuf->reserved[i] = cpu_to_le32(0);

fs/f2fs/f2fs.h

@@ -1214,10 +1214,9 @@ enum compress_algorithm_type {
 	COMPRESS_MAX,
 };
 
-#define COMPRESS_DATA_RESERVED_SIZE		4
+#define COMPRESS_DATA_RESERVED_SIZE		5
 struct compress_data {
 	__le32 clen;			/* compressed data size */
-	__le32 chksum;			/* checksum of compressed data */
 	__le32 reserved[COMPRESS_DATA_RESERVED_SIZE];	/* reserved */
 	u8 cdata[];			/* compressed data */
 };