drm/i915/gvt: Fix a memory leak in intel_gvt_init_gtt()

It will causes memory leak, if the function setup_spt_oos() fail,
in the function intel_gvt_init_gtt(),
which allocated by get_zeroed_page() and mapped by dma_map_page().

Unmap and free the page,  after STP oos initialize fail,
it will fix this issue.
Signed-off-by: Zhou, Wenjia <zhiyuan_zhu@htc.com>
Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>

drivers/gpu/drm/i915/gvt/gtt.c

@@ -2259,6 +2259,8 @@ int intel_gvt_init_gtt(struct intel_gvt *gvt)
 		ret = setup_spt_oos(gvt);
 		if (ret) {
 			gvt_err("fail to initialize SPT oos\n");
+			dma_unmap_page(dev, daddr, 4096, PCI_DMA_BIDIRECTIONAL);
+			__free_page(gvt->gtt.scratch_ggtt_page);
 			return ret;
 		}
 	}