drm/tidss: Fix race condition while handling interrupt registers

The driver has a spinlock for protecting the irq_masks field and irq
enable registers. However, the driver misses protecting the irq status
registers which can lead to races.

Take the spinlock when accessing irqstatus too.

Fixes: 32a1795f ("drm/tidss: New driver for TI Keystone platform Display SubSystem")
Cc: stable@vger.kernel.org
Signed-off-by: Devarsh Thakkar <devarsht@ti.com>
[Tomi: updated the desc]
Reviewed-by: Jonathan Cormier <jcormier@criticallink.com>
Tested-by: Jonathan Cormier <jcormier@criticallink.com>
Reviewed-by: Aradhya Bhatia <aradhya.bhatia@linux.dev>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20241021-tidss-irq-fix-v1-6-82ddaec94e4a@ideasonboard.com