mfd: Fix initialisation of tps65910 interrupts

Fix regression introduced by commit
a2974732 (TPS65911: Add new irq
definitions) which caused irq_num to be incorrectly set for tps65910.

Cc: stable@kernel.org
Signed-off-by: Johan Hovold <jhovold@gmail.com>
Acked-by: Graeme Gregory <gg@slimlogic.co.uk>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>