iolog: fix compile error for non-zlib

Signed-off-by: Jens Axboe <axboe@fb.com>
diff --git a/iolog.c b/iolog.c
index 45ef6be..19e96d2 100644
--- a/iolog.c
+++ b/iolog.c
@@ -897,6 +897,7 @@
 
 static int inflate_gz_chunks(struct io_log *log, FILE *f)
 {
+	return 0;
 }
 
 #endif