vts: Fix incorrect instance name in Teardown

The stopHostapd uses vendor HAL HIDL interface.
The interface name should use wifi_instance.

Bug: 161682236
Test: atest VtsHalWifiHostapdV1_2TargetTest
Change-Id: I8215cba3e2a36f48863f57e199684c7446e20692
Merged-In: I8215cba3e2a36f48863f57e199684c7446e20692
1 file changed