perf tools: Fix wrong message when running "make JOBS=1"

perf tools: Fix wrong message when running "make JOBS=1"

There is only one job when running "make JOBS=1", it should
print "sequential build" rather than "parallel build".

Before:

$ cd tools/perf && make JOBS=1
  BUILD:   Doing 'make -j1' parallel build

After:

$ cd tools/perf && make JOBS=1
  BUILD:   Doing 'make -j1' sequential build

Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://lore.kernel.org/lkml/20240730062301.23244-2-yangtiezhu@loongson.cn
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>