This reverts commit 5ac4f180.

Sorry for taking no notice that the function devlink_register() has been
already declared as void, so it is needs to revert this patch.
Signed-off-by: Guangbin Huang <huangguangbin2@huawei.com>
Link: https://lore.kernel.org/r/20211204012448.51360-1-huangguangbin2@huawei.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>