drm/vblank: Use spin_(un)lock_irq() in drm_crtc_vblank_reset()

All of the drivers in the kernel tree only call this from one of the
following contexts:

* drm_crtc_funcs->reset
* During initial module load

Since both of these contexts are guaranteed to have interrupts enabled
beforehand, there's no need to use the irqsave/irqrestore variants of
spin_(un)lock(). So, fix this to make the irq context of this function
more obvious.
Signed-off-by: Lyude Paul <lyude@redhat.com>
Cc: Daniel Vetter <daniel@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20200720190736.180297-2-lyude@redhat.comReviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/drm_vblank.c

@@ -1363,11 +1363,10 @@ EXPORT_SYMBOL(drm_crtc_vblank_off);
 void drm_crtc_vblank_reset(struct drm_crtc *crtc)
 {
 	struct drm_device *dev = crtc->dev;
-	unsigned long irqflags;
 	unsigned int pipe = drm_crtc_index(crtc);
 	struct drm_vblank_crtc *vblank = &dev->vblank[pipe];
 
-	spin_lock_irqsave(&dev->vbl_lock, irqflags);
+	spin_lock_irq(&dev->vbl_lock);
 	/*
 	 * Prevent subsequent drm_vblank_get() from enabling the vblank
 	 * interrupt by bumping the refcount.
@@ -1376,7 +1375,7 @@ void drm_crtc_vblank_reset(struct drm_crtc *crtc)
 		atomic_inc(&vblank->refcount);
 		vblank->inmodeset = 1;
 	}
-	spin_unlock_irqrestore(&dev->vbl_lock, irqflags);
+	spin_unlock_irq(&dev->vbl_lock);
 
 	drm_WARN_ON(dev, !list_empty(&dev->vblank_event_list));
 	drm_WARN_ON(dev, !list_empty(&vblank->pending_work));