md: extend disks_mutex coverage

mainline inclusion
from mainline-v5.16-rc1
commit 94f3cd7d
category: bugfix
bugzilla: 188015, https://gitee.com/openeuler/kernel/issues/I6OERX
CVE: NA

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next.git/commit/?id=94f3cd7d832c28681f1dea54b4dd8606e5e2bc75



--------------------------------

disks_mutex is intended to serialize md_alloc.  Extended it to also cover
the kobject_uevent call and getting the sysfs dirent to help reducing
error handling complexity.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

Conflict:
	drivers/md/md.c

Signed-off-by: Li Nan <linan122@huawei.com>
Reviewed-by: Hou Tao <houtao1@huawei.com>
Signed-off-by: Yongqiang Liu <liuyongqiang13@huawei.com>