enc28j60: don't specify (wrong) IRQ type

Recent changes to the IRQ framework have made passing the wrong
trigger type to request_irq() become a fatal error.  In the case
of the enc28j60 driver, it stopped working in my test harness.

(Specifically:  the signal detects "pin change" events, both edges,
not just falling edges.  Similarly, other boards might route it
through an inverter.  Trigger type are board-specific.)

This fixes that problem by the usual fix of expecting board setup
code to have set up the correct IRQ trigger type.  The best known
example of that being x86 setup.

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>