x86: avoid warning if memory is attached twice

Issue #1848

repos/os/src/drivers/platform/spec/x86/device_pd/main.cc

@@ -105,6 +105,9 @@ void Platform::Device_pd_component::attach_dma_mem(Genode::Dataspace_capability
 		page = rm_session()->attach_at(ds_cap, phys);
 	} catch (Rm_session::Out_of_metadata) {
 		throw;
+	} catch (Rm_session::Region_conflict) {
+		/* memory already attached before - done */
+		return;
 	} catch (...) { }
 
 	/* sanity check */