perf record: Simplify perf_record__write

1. Since all callers either test if it is less than zero or assign its
   result to an int variable, convert it from ssize_t to int;

2. There is just one use for the 'session' variable, so use rec->session
   directly instead;

3. No need to store the result of perf_data_file__write, since that
   result is either 'size' or -1, the later making the error result to
   be stored in 'errno' and accessed thru printf's %m in the pr_err
   call.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/n/tip-xwsk964dp681fica3xlqhjin@git.kernel.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/builtin-record.c

@@ -76,19 +76,14 @@ struct perf_record {
 	long			samples;
 };
 
-static ssize_t perf_record__write(struct perf_record *rec,
-				  void *buf, size_t size)
+static int perf_record__write(struct perf_record *rec, void *bf, size_t size)
 {
-	struct perf_session *session = rec->session;
-	ssize_t ret;
-
-	ret = perf_data_file__write(session->file, buf, size);
-	if (ret < 0) {
+	if (perf_data_file__write(rec->session->file, bf, size) < 0) {
 		pr_err("failed to write perf data, error: %m\n");
 		return -1;
 	}
 
-	rec->bytes_written += ret;
+	rec->bytes_written += size;
 	return 0;
 }