usbnet: fix error return code in usbnet_probe()

Return error code if usb_maxpacket() returns 0 in usbnet_probe()

Fixes: 397430b5 ("usbnet: sanity check for maxpacket")
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Wang Hai <wanghai38@huawei.com>
Reviewed-by: Johan Hovold <johan@kernel.org>
Link: https://lore.kernel.org/r/20211026124015.3025136-1-wanghai38@huawei.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>