drm/i915/gvt: return error on cmd access

If a register is not cmd accessible, should not just print error
message. Return error here so as not to deliver this cmd.

v2: return -EBADRQC to align with return value elsewhere. (kevin tian)
Signed-off-by: Zhao Yan <yan.y.zhao@intel.com>
Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>

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

@@ -874,7 +874,7 @@ static int cmd_reg_handler(struct parser_exec_state *s,
 	if (!intel_gvt_mmio_is_cmd_access(gvt, offset)) {
 		gvt_vgpu_err("%s access to non-render register (%x)\n",
 				cmd, offset);
-		return 0;
+		return -EBADRQC;
 	}
 
 	if (is_shadowed_mmio(offset)) {