drm: adp: Use spin_lock_irqsave for drm device event_lock

The lock is used in the interrupt handler so use spin_lock_irqsave to
disable interrupts and avoid deadlocks with the irq handler.

Fixes: 332122eb ("drm: adp: Add Apple Display Pipe driver")
Reviewed-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
Signed-off-by: Janne Grunau <j@jannau.net>
Link: https://lore.kernel.org/r/20250428-drm_adp_fixes-v2-1-912e081e55d8@jannau.net


Signed-off-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>