drm/vmwgfx: return -EFAULT for copy_to_user errors

copy_to/from_user() returns the number of bytes remaining to be copied
but we want to return a negative error code here.  This gets returned to
userspace.

Signed-off-by: Dan Carpenter <error27@gmail.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>
diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_execbuf.c b/drivers/gpu/drm/vmwgfx/vmwgfx_execbuf.c
index bdd67cf..8e39685 100644
--- a/drivers/gpu/drm/vmwgfx/vmwgfx_execbuf.c
+++ b/drivers/gpu/drm/vmwgfx/vmwgfx_execbuf.c
@@ -644,6 +644,7 @@
 	ret = copy_from_user(cmd, user_cmd, arg->command_size);
 
 	if (unlikely(ret != 0)) {
+		ret = -EFAULT;
 		DRM_ERROR("Failed copying commands.\n");
 		goto out_commit;
 	}