[ Upstream commit 60be976ac45137657b7b505d7e0d44d0e51accb7 ] dev_hard_header() returns the length of the header, so we need to test for negative errors rather than non-zero. Fixes: 889b7da23abf ("mctp: Add initial routing framework") Signed-off-by: Matt Johnston <matt@codeconstruct.com.au> Signed-off-by: David S. Miller <davem@davemloft.net> Signed-off-by: Sasha Levin <sashal@kernel.org>