Add explicit Result::ok() checks where needed

This is part of a large-scale cleanup to remove operator bool() from
android::base::expected. For more details, see aosp/1533001.

Bug: 176148206
Test: m checkbuild continuous_instrumentation_tests continuous_instrumentation_tests_api_coverage continuous_native_tests device-tests platform_tests
Exempt-From-Owner-Approval: mechanical large-scale change
Change-Id: Iec637c7019927485dd1d814d38471e617276764f