perf tools: Initialize perf_data_file fd field

Building the perf CTF converter fails with gcc 4.8.4 on Ubuntu 14.04
with the following error:

  error: missing initializer for field ‘fd’ of ‘struct perf_data_file’
  [-Werror=missing-field-initializers]

Per 4b838b0d ("perf tools: Add compression id into 'struct
kmod_path'") and the ensuing discussion on the mailing list, it appears
that this affects other distributions and gcc versions.
Signed-off-by: Jeremie Galarneau <jeremie.galarneau@efficios.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/20180829201648.19588-1-jeremie.galarneau@efficios.comSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/data-convert-bt.c

@@ -1578,7 +1578,7 @@ int bt_convert__perf2ctf(const char *input, const char *path,
 {
 	struct perf_session *session;
 	struct perf_data data = {
-		.file.path = input,
+		.file      = { .path = input, .fd = -1 },
 		.mode      = PERF_DATA_MODE_READ,
 		.force     = opts->force,
 	};