drm/panthor: Update panthor_mmu::irq::mask when needed

drm/panthor: Update panthor_mmu::irq::mask when needed

When we clear the faulty bits in the AS mask, we also need to update
the panthor_mmu::irq::mask field otherwise our IRQ handler won't get
called again until the GPU is reset.

Changes in v2:
- Add Liviu's R-b

Changes in v3:
- Add Steve's R-b

Fixes: 647810ec2476 ("drm/panthor: Add the MMU/VM logical block")
Reviewed-by: Liviu Dudau <liviu.dudau@arm.com>
Reviewed-by: Steven Price <steven.price@arm.com>
Link: https://lore.kernel.org/r/20250404080933.2912674-4-boris.brezillon@collabora.com
Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>