[SC92031]: Fix priv->lock context

The spin_lock calls made in dev->open and dev->close must disable
BH since open/close are made in process context.  Conversely, the
call in dev->hard_start_xmit does not need to disable BH since it
is already executing with BH disabled.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>