tests/i915/perf_pmu: Fix allow hang handling

Commit d7a74b95 ("tests/i915/perf_pmu: Convert to intel_ctx_t (v3)")
broke the test when it is run in its entirety.

Correct context id needs to be used with igt_allow_hang to avoid context
ban preventing the test to run to completion.

Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Fixes: d7a74b95 ("tests/i915/perf_pmu: Convert to intel_ctx_t (v3)")
Cc: Ashutosh Dixit <ashutosh.dixit@intel.com>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Reviewed-by: Ashutosh Dixit <ashutosh.dixit@intel.com>