rnbd-srv: Convert to use bdev_open_by_path()

mainline inclusion
from mainline-v6.7-rc1
commit c2114f11a30ede1d1dbab09dab6e6f4024bb2fbb
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I8KPBR
CVE: NA

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?h=v6.7-rc3&id=c2114f11a30ede1d1dbab09dab6e6f4024bb2fbb



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

Convert rnbd-srv to use bdev_open_by_path() and pass the handle
around.

CC: Jack Wang <jinpu.wang@ionos.com>
CC: "Md. Haris Iqbal" <haris.iqbal@ionos.com>
Acked-by: "Md. Haris Iqbal" <haris.iqbal@ionos.com>
Acked-by: Christoph Hellwig <hch@lst.de>
Acked-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Jan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/20230927093442.25915-6-jack@suse.cz


Signed-off-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Li Lingfeng <lilingfeng3@huawei.com>