[PATCH] drm/nouveau: fix another lock unbalance in nouveau_crtc_page_flip

[Maarten Lankhorst <maarten.lankhorst@canonical.com>]

Fixes a regression introduced by 060810d7abaabca "drm/nouveau: fix locking issues in page flipping paths".
chan->cli->mutex is unlocked a second time in the fail_unreserve path, fix this by moving mutex_unlock down.

Cc: stable@vger.kernel.org # v3.11+
---
diff --git a/drivers/gpu/drm/nouveau/nouveau_display.c b/drivers/gpu/drm/nouveau/nouveau_display.c
index 24011596af43..5524a3705224 100644
--- a/drivers/gpu/drm/nouveau/nouveau_display.c
+++ b/drivers/gpu/drm/nouveau/nouveau_display.c
@@ -762,9 +762,9 @@ nouveau_crtc_page_flip(struct drm_crtc *crtc, struct drm_framebuffer *fb,
  	}
  
  	ret = nouveau_page_flip_emit(chan, old_bo, new_bo, s, &fence);
-	mutex_unlock(&chan->cli->mutex);
  	if (ret)
  		goto fail_unreserve;
+	mutex_unlock(&chan->cli->mutex);
  
  	/* Update the crtc struct and cleanup */
  	crtc->fb = fb;