fsck.f2fs: export valid image size

Change to calculate and export max image size with valid blocks
used of image rather than last used block of image.

[FSCK] Max image size: xx MB, Free space: xx MB

Signed-off-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
4 files changed