drm/i915: Drop struct_mutex guard from debugfs/framebuffer_info

It protects nothing being accessed for the intel_framebuffer, so it's
own locking had better be sufficient.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191004134015.13204-17-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/i915_debugfs.c

@@ -1534,11 +1534,6 @@ static int i915_gem_framebuffer_info(struct seq_file *m, void *data)
 	struct drm_device *dev = &dev_priv->drm;
 	struct intel_framebuffer *fbdev_fb = NULL;
 	struct drm_framebuffer *drm_fb;
-	int ret;
-
-	ret = mutex_lock_interruptible(&dev->struct_mutex);
-	if (ret)
-		return ret;
 
 #ifdef CONFIG_DRM_FBDEV_EMULATION
 	if (dev_priv->fbdev && dev_priv->fbdev->helper.fb) {
@@ -1573,7 +1568,6 @@ static int i915_gem_framebuffer_info(struct seq_file *m, void *data)
 		seq_putc(m, '\n');
 	}
 	mutex_unlock(&dev->mode_config.fb_lock);
-	mutex_unlock(&dev->struct_mutex);
 
 	return 0;
 }