net: socionext: Fix a signedness bug in ave_probe()

net: socionext: Fix a signedness bug in ave_probe()

[ Upstream commit 7f9e88e6ef8c971f2c638b5ff7044c59b5d0f58d ]

The "phy_mode" variable is an enum and in this context GCC treats it as
an unsigned int so the error handling is never triggered.

Fixes: 4c270b55a5af ("net: ethernet: socionext: add AVE ethernet driver")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Kunihiko Hayashi <hayashi.kunihiko@socionext.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>