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>
diff --git a/drivers/gpu/drm/qxl/qxl_prime.c b/drivers/gpu/drm/qxl/qxl_prime.c
index 3d031b5..9f029dd 100644
--- a/drivers/gpu/drm/qxl/qxl_prime.c
+++ b/drivers/gpu/drm/qxl/qxl_prime.c
@@ -68,5 +68,5 @@
 		       struct vm_area_struct *area)
 {
 	WARN_ONCE(1, "not implemented");
-	return ENOSYS;
+	return -ENOSYS;
 }