drm/qxl: fix erroneous return value

The qxl_gem_prime_mmap() function returns ENOSYS instead of -ENOSYS
Signed-off-by: Anton Protopopov <a.s.protopopov@gmail.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/qxl/qxl_prime.c

@@ -68,5 +68,5 @@ int qxl_gem_prime_mmap(struct drm_gem_object *obj,
 		       struct vm_area_struct *area)
 {
 	WARN_ONCE(1, "not implemented");
-	return ENOSYS;
+	return -ENOSYS;
 }