asix: Add check for usbnet_get_endpoints

Add check for usbnet_get_endpoints() and return the error if it fails
in order to transfer the error.

Fixes: 16626b0c

 ("asix: Add a new driver for the AX88172A")
Signed-off-by: Chen Ni <nichen@iscas.ac.cn>
Signed-off-by: David S. Miller <davem@davemloft.net>