ext3: get rid of the duplicate code on ext3_fill_super

Setting s_mount_opt to 0 is unnecessary because we use kzalloc() for sb
allocation. s_resuid and s_resgid are set again few lines below based on
values in on disk superblock.

Signed-off-by: Zhao Hongjiang <zhaohongjiang@huawei.com>
Signed-off-by: Jan Kara <jack@suse.cz>