sierra_net: Endianess bug fix.

I discovered I couldn't get sierra_net to work on a powerpc.  Turns out
the firmware attribute check assumes the system is little endian and
hence fails because the attributes is a 16 bit value.

Signed-off-by: Len Sorensen <lsorense@csclub.uwaterloo.ca>
Signed-off-by: David S. Miller <davem@davemloft.net>