drm/crc-debugfs: Also sprinkle irqrestore over early exits

drm/crc-debugfs: Also sprinkle irqrestore over early exits

I. was. blind.

Caught with vkms, which has some really slow crc computation function.

Fixes: e76aca4a42b1 ("drm/crc-debugfs: User irqsafe spinlock in drm_crtc_add_crc_entry")
Cc: Rodrigo Siqueira <rodrigosiqueiramelo@gmail.com>
Cc: Tomeu Vizoso <tomeu.vizoso@collabora.com>
Cc: Emil Velikov <emil.velikov@collabora.com>
Cc: Benjamin Gaignard <benjamin.gaignard@linaro.org>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Emil Velikov <emil.velikov@collabora.com>
Reviewed-by: Benjamin Gaignard <benjamin.gaignard@linaro.org>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190606211544.5389-1-daniel.vetter@ffwll.ch