net: lpc-enet: fix error return code in lpc_mii_init()

[ Upstream commit 88ec7cb22ddde725ed4ce15991f0bd9dd817fd85 ]

Fix to return a negative error code from the error handling
case instead of 0, as done elsewhere in this function.

Fixes: b7370112 ("lpc32xx: Added ethernet driver")
Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Acked-by: Vladimir Zapolskiy <vz@mleia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>