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

tools/Makefile

···
 	$(call descend,lib/subcmd,clean)
 
 perf_clean:
-	$(call descend,$(@:_clean=),clean)
+	$(Q)mkdir -p $(PERF_O) .
+	$(Q)$(MAKE) --no-print-directory -C perf O=$(PERF_O) subdir= clean
 
 selftests_clean:
 	$(call descend,testing/$(@:_clean=),clean)