drm/i915: Drop irqsave/restore for flip_done_handler()

Since flip_done_handler() is always called from the irq handler
we can skip the irqsave/restore dance.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230928152450.30109-2-ville.syrjala@linux.intel.com


Reviewed-by: Arun R Murthy <arun.r.murthy@intel.com>