drivers/net/usb/asix.c: Fix pointer cast.

Stephen Rothwell reports the following new warning:

drivers/net/usb/asix.c: In function 'asix_rx_fixup':
drivers/net/usb/asix.c:325: warning: cast from pointer to integer of different size
drivers/net/usb/asix.c:354: warning: cast from pointer to integer of different size

The code just cares about the low alignment bits, so use
an "unsigned long" cast instead of one to "u32".

Signed-off-by: David S. Miller <davem@davemloft.net>