perf test pmu: Set uninitialized PMU alias to null

Commit 3e0bf9fd ("perf pmu: Restore full PMU name wildcard
support") adds a test case "PMU cmdline match" that covers PMU name
wildcard support provided by function perf_pmu__match().

The test works with a wide range of supported combinations of PMU name
matching but omits the case that if the perf_pmu__match() cannot match
the PMU name to the wildcard, it tries to match its alias. However, this
variable is not set up, causing the test case to fail when run with
subprocesses or to segfault if run as a single process.

  ./perf test -vv 9
    9: Sysfs PMU tests                                :
    9.1: Parsing with PMU format directory            : Ok
    9.2: Parsing with PMU event                       : Ok
    9.3: PMU event names                              : Ok
    9.4: PMU name combining                           : Ok
    9.5: PMU name comparison                          : Ok
    9.6: PMU cmdline match                            : FAILED!

  ./perf test -F 9
    9.1: Parsing with PMU format directory            : Ok
    9.2: Parsing with PMU event                       : Ok
    9.3: PMU event names                              : Ok
    9.4: PMU name combining                           : Ok
    9.5: PMU name comparison                          : Ok
  Segmentation fault (core dumped)

Initialize the PMU alias to null for all tests of perf_pmu__match()
as this functionality is not being tested and the alias matching works
exactly the same as the matching of the PMU name.

./perf test -F 9
  9.1: Parsing with PMU format directory                             : Ok
  9.2: Parsing with PMU event                                        : Ok
  9.3: PMU event names                                               : Ok
  9.4: PMU name combining                                            : Ok
  9.5: PMU name comparison                                           : Ok
  9.6: PMU cmdline match                                             : Ok

Fixes: 3e0bf9fd ("perf pmu: Restore full PMU name wildcard support")
Signed-off-by: Veronika Molnarova <vmolnaro@redhat.com>
Cc: James Clark <james.clark@linaro.org>
Cc: Michael Petlan <mpetlan@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Radostin Stoyanov <rstoyano@redhat.com>
Link: https://lore.kernel.org/r/20240808103749.9356-1-vmolnaro@redhat.com


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