f2fs: align data types between on-disk and in-memory block addresses

The on-disk block address is defined as __le32, but in-memory block address,
block_t, does as u64.

Let's synchronize them to 32 bits.

Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Jaegeuk Kim <jaegeuk.kim@samsung.com>
diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
index 7b05029..92fd4e9 100644
--- a/fs/f2fs/f2fs.h
+++ b/fs/f2fs/f2fs.h
@@ -37,7 +37,10 @@
 		typecheck(unsigned long long, b) &&			\
 		((long long)((a) - (b)) > 0))
 
-typedef u64 block_t;
+typedef u32 block_t;	/*
+			 * should not change u32, since it is the on-disk block
+			 * address format, __le32.
+			 */
 typedef u32 nid_t;
 
 struct f2fs_mount_info {