perf tests pmu: Initialize all fields of test_pmu variable

Instead of explicitely initializing just the .name and .alias_name,
use struct member named initialization of just the non-null -name field,
the compiler will initialize all the other non-explicitely initialized
fields to NULL.

This makes the code more robust, avoiding the error recently fixed when
the .alias_name was used and contained a random value.

Reviewed-by: Veronika Molnarova <vmolnaro@redhat.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Ian Rogers <irogers@google.com>
Cc: James Clark <james.clark@arm.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Kan Liang <kan.liang@linux.intel.com>
Cc: Michael Petlan <mpetlan@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Radostin Stoyanov <rstoyano@redhat.com>
Link: https://lore.kernel.org/lkml/e26941f9-f86c-4f2e-b812-20c49fb2c0d3@redhat.com


Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>