Btrfs: use linux/sizes.h to represent constants

We use many constants to represent size and offset value.  And to make
code readable we use '256 * 1024 * 1024' instead of '268435456' to
represent '256MB'.  However we can make far more readable with 'SZ_256MB'
which is defined in the 'linux/sizes.h'.

So this patch replaces 'xxx * 1024 * 1024' kind of expression with
single 'SZ_xxxMB' if 'xxx' is a power of 2 then 'xxx * SZ_1M' if 'xxx' is
not a power of 2. And I haven't touched to '4096' & '8192' because it's
more intuitive than 'SZ_4KB' & 'SZ_8KB'.

Signed-off-by: Byongho Lee <bhlee.kernel@gmail.com>
Signed-off-by: David Sterba <dsterba@suse.com>
diff --git a/fs/btrfs/disk-io.h b/fs/btrfs/disk-io.h
index adeb318..a407d1b 100644
--- a/fs/btrfs/disk-io.h
+++ b/fs/btrfs/disk-io.h
@@ -19,7 +19,7 @@
 #ifndef __DISKIO__
 #define __DISKIO__
 
-#define BTRFS_SUPER_INFO_OFFSET (64 * 1024)
+#define BTRFS_SUPER_INFO_OFFSET SZ_64K
 #define BTRFS_SUPER_INFO_SIZE 4096
 
 #define BTRFS_SUPER_MIRROR_MAX	 3
@@ -35,7 +35,7 @@
 
 static inline u64 btrfs_sb_offset(int mirror)
 {
-	u64 start = 16 * 1024;
+	u64 start = SZ_16K;
 	if (mirror)
 		return start << (BTRFS_SUPER_MIRROR_SHIFT * mirror);
 	return BTRFS_SUPER_INFO_OFFSET;