net: broadcom/bcmsysport: Fix signedness in bcm_sysport_probe()

net: broadcom/bcmsysport: Fix signedness in bcm_sysport_probe()

[ Upstream commit 25a584955f020d6ec499c513923fb220f3112d2b ]

The "priv->phy_interface" variable is an enum and in this context GCC
will treat it as unsigned so the error handling will never be
triggered.

Fixes: 80105befdb4b ("net: systemport: add Broadcom SYSTEMPORT Ethernet MAC driver")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Acked-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>