usbnet: smsc75xx: Merge memcpy + le32_to_cpus to get_unaligned_le32

Merge the combo use of memcpy and le32_to_cpus.
Use get_unaligned_le32 instead.
This simplifies the code.

Signed-off-by: Chuhong Yuan <hslester96@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>