drm/vmwgfx: Fix recently introduced sparse / smatch warnings and errors

Reported-by: Fengguang Wu <fengguang.wu@intel.com>
Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>
Reviewed-by: Jakob Bornecrant <jakob@vmware.com>
diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_drv.c b/drivers/gpu/drm/vmwgfx/vmwgfx_drv.c
index 078b9b0..9893328 100644
--- a/drivers/gpu/drm/vmwgfx/vmwgfx_drv.c
+++ b/drivers/gpu/drm/vmwgfx/vmwgfx_drv.c
@@ -680,8 +680,10 @@
 		dev_priv->prim_bb_mem = dev_priv->vram_size;
 
 	ret = vmw_dma_masks(dev_priv);
-	if (unlikely(ret != 0))
+	if (unlikely(ret != 0)) {
+		mutex_unlock(&dev_priv->hw_mutex);
 		goto out_err0;
+	}
 
 	if (unlikely(dev_priv->prim_bb_mem < dev_priv->vram_size))
 		dev_priv->prim_bb_mem = dev_priv->vram_size;