perf build: Use FEATURE-DUMP instead of PERF-FEATURES in the .gitignore file

Since commit 4ae61202 ("perf build: Rename PERF-FEATURES into
FEATURE-DUMP") renames PERF-FEATURES into FEATURE-DUMP, the .gitignore
file should also do this thing for consistency.
Signed-off-by: Yunlong Song <yunlong.song@huawei.com>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/r/1426821638-11227-2-git-send-email-yunlong.song@huawei.comSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/.gitignore

 PERF-CFLAGS
 PERF-GUI-VARS
 PERF-VERSION-FILE
-PERF-FEATURES
+FEATURE-DUMP
 perf
 perf-read-vdso32
 perf-read-vdsox32