f2fs: compress: fix to avoid inconsistence bewteen i_blocks and dnode

In reserve_compress_blocks(), we update blkaddrs of dnode in prior to
inc_valid_block_count(), it may cause inconsistent status bewteen
i_blocks and blkaddrs once inc_valid_block_count() fails.

To fix this issue, it needs to reverse their invoking order.

Fixes: c75488fb ("f2fs: introduce F2FS_IOC_RESERVE_COMPRESS_BLOCKS")
Reviewed-by: Daeho Jeong <daehojeong@google.com>
Signed-off-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>