iris: take a reference to memobj bo in iris_resource_from_memobj

v2: and remove it from iris_memobj_create_from_handle ... (Nanley)

Closes: #4969
Fixes: 772dc50d

 ("iris: hook up resource creation from memory object")
Signed-off-by: Tapani Pälli <tapani.palli@intel.com>
Reviewed-by: Nanley Chery <nanley.g.chery@intel.com>
Part-of: <!11552>

src/gallium/drivers/iris/iris_resource.c

@@ -334,8 +334,6 @@ iris_memobj_create_from_handle(struct pipe_screen *pscreen,
    memobj->format = whandle->format;
    memobj->stride = whandle->stride;
 
-   iris_bo_reference(memobj->bo);
-
    return &memobj->b;
 }
 
@@ -1253,6 +1251,8 @@ iris_resource_from_memobj(struct pipe_screen *pscreen,
    res->offset = offset;
    res->external_format = memobj->format;
 
+   iris_bo_reference(memobj->bo);
+
    return &res->base.b;
 }