tools build: Fix perf_clean target

tools build: Fix perf_clean target

Fix perf_clean target to follow the same logic as perf target.

Fixes the following make invokation:

  $ cd <kernelsrc> && make tools/perf_clean

Reported-by: TJ <[email protected]>
Signed-off-by: Jiri Olsa <[email protected]>
Tested-by: Arnaldo Carvalho de Melo <[email protected]>
Cc: David Ahern <[email protected]>
Cc: Namhyung Kim <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=116411
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Arnaldo Carvalho de Melo <[email protected]>