sfc: Do not reinitialise XAUI serdes before it has completed reset

falcon_reset_xaui() waits for XGXS reset to complete, but the XAUI
serdes reset may take longer.  It needs to check both reset active
bits.

Signed-off-by: Ben Hutchings <bhutchings@solarflare.com>
Signed-off-by: David S. Miller <davem@davemloft.net>