[WifiAutoUpdateTest] Fix for getting the buildid

Bug: 152757180
Test: Verified the changes
Change-Id: Ifdfbdb319c27ff98f760209f4f22be8fc3029ef4
diff --git a/acts/tests/google/wifi/WifiAutoUpdateTest.py b/acts/tests/google/wifi/WifiAutoUpdateTest.py
index 625b491..8317800 100755
--- a/acts/tests/google/wifi/WifiAutoUpdateTest.py
+++ b/acts/tests/google/wifi/WifiAutoUpdateTest.py
@@ -126,7 +126,7 @@
         self.wifi_hotspot = {"SSID": "hotspot_%s" % utils.rand_ascii_str(6),
                              "password": "pass_%s" % utils.rand_ascii_str(6)}
         band = WIFI_CONFIG_APBAND_5G
-        if self.dut.build_id.startswith("Q"):
+        if self.dut.build_info["build_id"].startswith("Q"):
             band = WifiEnums.WIFI_CONFIG_APBAND_5G_OLD
         wutils.save_wifi_soft_ap_config(self.dut, self.wifi_hotspot, band)