super1: Clear extra flags when initializing metadata

super1: Clear extra flags when initializing metadata

When adding a disk to a RAID1 array, the metadata is read from the
existing member disks for sync. However, only the bad_blocks flag are
copied, the bad_blocks records are not copied, so the bad_blocks
records are all zeros. The kernel function super_1_load() detects
bad_blocks flag and reads the bad_blocks record, then sets the bad
block using badblocks_set().

After the kernel commit 1726c7746783 (badblocks: improve badblocks_set()
for multiple ranges handling) if the length of a bad_blocks record is 0,
it will return a failure. Therefore the device addition will fail.

So when adding a new disk, some flags cannot be sync and need to be clead.

Signed-off-by: Wu Guanghao <wuguanghao3@huawei.com>