net: axienet: fix a signedness bug in probe

net: axienet: fix a signedness bug in probe

[ Upstream commit 73e211e11be86715d66bd3c9d38b3c34b05fca9a ]

The "lp->phy_mode" is an enum but in this context GCC treats it as an
unsigned int so the error handling is never triggered.

Fixes: ee06b1728b95 ("net: axienet: add support for standard phy-mode binding")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Radhey Shyam Pandey <radhey.shyam.pandey@xilinx.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>