drm/i915/guc: Flush the residual log capture irq on disabling

drm/i915/guc: Flush the residual log capture irq on disabling

As we disable the log capture events, flush any residual interrupt
before we flush and disable the worker.

v2: Mika pointed out that it wasn't the worker re-queueing itself, but a
rogue irq.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=109716
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190221163833.21393-1-chris@chris-wilson.co.uk