net: phy: propagate an error back to the callers of phy_sfp_probe

net: phy: propagate an error back to the callers of phy_sfp_probe

The compilation warning below reveals that the errors returned from
the sfp_bus_add_upstream() call are not propagated to the callers.
Fix it by returning "ret".

14:37:51 drivers/net/phy/phy_device.c: In function 'phy_sfp_probe':
14:37:51 drivers/net/phy/phy_device.c:1236:6: warning: variable 'ret'
   set but not used [-Wunused-but-set-variable]
14:37:51  1236 |  int ret;
14:37:51       |      ^~~

Fixes: 298e54fa810e ("net: phy: add core phylib sfp support")
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>