RDMA/mlx5: Fix NULL string error

stable inclusion
from stable-v5.10.198
commit cfc333393ae66fe00b84c6917bc44f93bedb638a
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I987V5

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=cfc333393ae66fe00b84c6917bc44f93bedb638a



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commit dab994bc upstream.

checkpath is complaining about NULL string, change it to 'Unknown'.

Fixes: 37aa5c36 ("IB/mlx5: Add UARs write-combining and non-cached mapping")
Signed-off-by: Shay Drory <shayd@nvidia.com>
Link: https://lore.kernel.org/r/8638e5c14fadbde5fa9961874feae917073af920.1695203958.git.leonro@nvidia.com


Signed-off-by: Leon Romanovsky <leon@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: sanglipeng <sanglipeng1@jd.com>