perf scripts perl: Makefile fix

Fix a typo introduced by recent Makefile changes, in f9af3a4.  Without it, Perl
scripting support won't get compiled in.

Cc: Frédéric Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Stephane Eranian <eranian@google.com>
LKML-Reference: <1276836006.7762.15.camel@tropicana>
Signed-off-by: Tom Zanussi <tzanussi@gmail.com>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>