perf tools: Pass full path of FEATURES_DUMP

When building with an external FEATURES_DUMP, bpf complains
that features dump file is not found. Fix it by passing full file path.
Signed-off-by: David Carrillo-Cisneros <davidcc@google.com>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Paul Turner <pjt@google.com>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/r/20170827075442.108534-7-davidcc@google.comSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/Makefile.perf

@@ -240,7 +240,7 @@ endif
 ifeq ($(FEATURES_DUMP),)
 FEATURE_DUMP_EXPORT := $(realpath $(OUTPUT)FEATURE-DUMP)
 else
-FEATURE_DUMP_EXPORT := $(FEATURES_DUMP)
+FEATURE_DUMP_EXPORT := $(realpath $(FEATURES_DUMP))
 endif
 
 export prefix bindir sharedir sysconfdir DESTDIR