Revert "net: devlink: add RNLT lock assertion to devlink_compat_switch_id_get()"

This reverts commit 6005a8ae.

The assertion was intentionally removed in commit 043b8413

 ("net:
devlink: remove redundant rtnl lock assert") and, contrary what is
described in the commit message, the comment reflects that: "Caller must
hold RTNL mutex or reference to dev...".

Signed-off-by: Vlad Buslov <vladbu@nvidia.com>
Tested-by: Leon Romanovsky <leonro@nvidia.com>
Link: https://lore.kernel.org/r/20220829121324.3980376-1-vladbu@nvidia.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>