i915: return -EFAULT if copy_to_user fails

copy_to_user() returns the number of bytes remaining to be copied and
I'm pretty sure we want to return a negative error code here.

Signed-off-by: Dan Carpenter <error27@gmail.com>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: stable@kernel.org
diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index 68526f4..748c263 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -3588,6 +3588,7 @@
 		if (ret != 0) {
 			DRM_ERROR("copy %d cliprects failed: %d\n",
 				  args->num_cliprects, ret);
+			ret = -EFAULT;
 			goto pre_mutex_err;
 		}
 	}