f2fs: convert dev_valid_block_count to void
f2fs: convert dev_valid_block_count to void

Signed-off-by: Gu Zheng <9eae2d327ddc4c2ff66f290d0aa6288f14fc5928@cn.fujitsu.com>
Signed-off-by: Jaegeuk Kim <20424effba9d4aeeb410130c5f23aa328fa29e09@samsung.com>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs