md: fix return value of rdev_size_change()

When trying to grow an array by enlarging component devices,
rdev_size_store() expects the return value of rdev_size_change() to be
in sectors, but the actual value is returned in KBs.

This functionality was broken by commit
     dd8ac336c13fd8afdb082ebacb1cddd5cf727889
so this patch is suitable for any kernel since 2.6.30.

Cc: stable@kernel.org
Signed-off-by: Justin Maggard <jmaggard10@gmail.com>
Signed-off-by: NeilBrown <neilb@suse.de>

drivers/md/md.c

@@ -1337,7 +1337,7 @@ super_90_rdev_size_change(mdk_rdev_t *rdev, sector_t num_sectors)
 	md_super_write(rdev->mddev, rdev, rdev->sb_start, rdev->sb_size,
 		       rdev->sb_page);
 	md_super_wait(rdev->mddev);
-	return num_sectors / 2; /* kB for sysfs */
+	return num_sectors;
 }
 
 
@@ -1704,7 +1704,7 @@ super_1_rdev_size_change(mdk_rdev_t *rdev, sector_t num_sectors)
 	md_super_write(rdev->mddev, rdev, rdev->sb_start, rdev->sb_size,
 		       rdev->sb_page);
 	md_super_wait(rdev->mddev);
-	return num_sectors / 2; /* kB for sysfs */
+	return num_sectors;
 }
 
 static struct super_type super_types[] = {