declance: Remove a dangling spin_unlock_irq() thingy

 The spin_unlock_irq() invocation in lance_start_xmit() has no matching
locking request.  The call is already protected by netif_tx_lock, so
remove the statement.

Signed-off-by: Maciej W. Rozycki <macro@linux-mips.org>
Signed-off-by: Jeff Garzik <jeff@garzik.org>