net: ethernet: xilinx: use of_property_read_bool() instead of of_get_property

"little-endian" has no specific content, use more helper function
of_property_read_bool() instead of of_get_property()

Signed-off-by: Wang Qing <wangqing@vivo.com>
Signed-off-by: David S. Miller <davem@davemloft.net>