arm/mach-integrator/time.c, mwave: revert portions of recent irq cleanups

The recent irq cleanups for arch/arm/mach-integrator/time.c and
drivers/char/mwave/tp3780i.c changed the request_irq() dev_id
parameter, but neglected to change the matching free_irq() parameter,
thus creating a bug upon irq de-registration.

Given that the impetus for the changes is not yet accepted upstream,
it is best to revert the irq cleanups.

Mostly.  A comment is added to time.c to reduce future confusion,
of type that led to my time.c cleanup in the first place.

Signed-off-by: Jeff Garzik <jgarzik@redhat.com>