Add the function f2fs_reserve_block() to easily reserve new blocks, and
use it to clean up more codes.
Signed-off-by: NHuajun Li <huajun.li@intel.com>
Signed-off-by: NHaicheng Li <haicheng.li@linux.intel.com>
Signed-off-by: NWeihong Xu <weihong.xu@intel.com>
Signed-off-by: NJaegeuk Kim <jaegeuk.kim@samsung.com>