perf test topology: Use !strncmp(right platform) to fix guest PPC comparision check

perf test topology: Use !strncmp(right platform) to fix guest PPC comparision check

commit e17bce7afd6131d0 ("perf test session topology: Fix test to skip
the test in guest environment") added check to skip the testcase if the
socket_id can't be fetched from topology info.

But the condition check uses strncmp which should be changed to !strncmp
and to correctly match platform.

Fix this condition check.

Fixes: e17bce7afd6131d0 ("perf test session topology: Fix test to skip the test in guest environment")
Reported-by: Thomas Richter <tmricht@linux.ibm.com>
Signed-off-by: Athira Jajeev <atrajeev@linux.vnet.ibm.com>
Acked-by: Ian Rogers <irogers@google.com>
Cc: Athira Rajeev <atrajeev@linux.vnet.ibm.com>
Cc: Disha Goel <disgoel@linux.vnet.ibm.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Kajol Jain <kjain@linux.ibm.com>
Cc: linuxppc-dev@lists.ozlabs.org
Cc: Madhavan Srinivasan <maddy@linux.ibm.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Nageswara R Sastry <rnsastry@linux.ibm.com>
Link: https://lore.kernel.org/r/20220610135939.63361-1-atrajeev@linux.vnet.ibm.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>