bus: ti-sysc: Fix wrong offset for display subsystem reset quirk

Commit 7324a7a0 ("bus: ti-sysc: Implement display subsystem reset
quirk") added support for DSS reset, but is using dispc offset also for
DSS also registers as reported by Tomi Valkeinen <tomi.valkeinen@ti.com>.
Also, we're not using dispc_offset for dispc IRQSTATUS register so let's
fix that too.

Fixes: 7324a7a0 ("bus: ti-sysc: Implement display subsystem reset quirk")
Reported-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Reviewed-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>