rbd: make get_lock_owner_info() return a single locker or NULL

stable inclusion
from stable-v5.10.193
commit 2547026bb8c45440115771353035d8287979e315
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I9399M

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=2547026bb8c45440115771353035d8287979e315



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[ Upstream commit f38cb9d9 ]

Make the "num_lockers can be only 0 or 1" assumption explicit and
simplify the API by getting rid of output parameters in preparation
for calling get_lock_owner_info() twice before blocklisting.

Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
Reviewed-by: Dongsheng Yang <dongsheng.yang@easystack.cn>
Stable-dep-of: 58815900 ("rbd: retrieve and check lock owner twice before blocklisting")
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: sanglipeng <sanglipeng1@jd.com>