f2fs: convert F2FS_I_SB to sbi in f2fs_setattr()

Introduce sbi in f2fs_setattr() and convert F2FS_I_SB to it. No logic
change, just cleanup and prepare to get CAP_BLKS_PER_SEC(sbi).

Signed-off-by: wangzijie <wangzijie1@honor.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>