net: rtnetlink: remove redundant assignment to variable err

[ Upstream commit 7d311801 ]

The variable err is being initializeed with a value that is never read
and it is being updated later with a new value. The initialization
is redundant and can be removed.

Addresses-Coverity: ("Unused value")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Stable-dep-of: bf29555f ("rtnetlink: Allow deleting FDB entries in user namespace")
Signed-off-by: Sasha Levin <sashal@kernel.org>