hw/sd.c: Set ILLEGAL_COMMAND for ACMDs in invalid state

App commands in an invalid state should set ILLEGAL_COMMAND, not
merely return a zero response.
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>
Signed-off-by: NAndrzej Zaborowski <andrew.zaborowski@intel.com>

hw/sd.c

@@ -1262,7 +1262,7 @@ static sd_rsp_type_t sd_app_command(SDState *sd,
     }
 
     fprintf(stderr, "SD: ACMD%i in a wrong state\n", req.cmd);
-    return sd_r0;
+    return sd_illegal;
 }
 
 static int cmd_valid_while_locked(SDState *sd, SDRequest *req)