net: broadcom: bcm4908_enet: fix endianness in xmit code

Use le32_to_cpu() for reading __le32 struct field filled by hw.

Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>