perf test: Fix bpf test sample mismatch reporting

When the expected sample count in the condition changed, the message
needs to be changed too, otherwise we'll get:

  0x1001f2091d8: mmap mask[0]:
  BPF filter result incorrect, expected 56, got 56 samples

Fixes: 4b04e0de ("perf test: Fix basic bpf filtering test")
Signed-off-by: Michael Petlan <mpetlan@redhat.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Sumanth Korikkar <sumanthk@linux.ibm.com>
Link: https //lore.kernel.org/r/20210805160611.5542-1-mpetlan@redhat.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>