net: lan78xx: Bail out if lan78xx_get_endpoints fails

We need to bail out if lan78xx_get_endpoints() fails, otherwise the
result is overwritten.

Fixes: 55d7de9d ("Microchip's LAN7800 family USB 2/3 to 10/100/1000 Ethernet")
Signed-off-by: Stefan Wahren <stefan.wahren@i2se.com>
Reviewed-by: Raghuram Chary Jallipalli <raghuramchary.jallipalli@microchip.com>
Signed-off-by: David S. Miller <davem@davemloft.net>