Fix VtsHalDrmV1_0Target test failure

DrmHalVendorFactoryTest.EmptyPluginUUIDNotSupported
was failing on 64 bit builds. The test was using
an uninitialized hidl_array as the empty UUID which
was incorrect. This change initializes the array
contents to null values.

Test: drm hal tests pass

bug: 37172151
Change-Id: I0acb86921f0daceba30fa7879980ce819db64a74