timerfd: call osmo_fd_unregister() when closing on read error

Change-Id: I8513126286083ebf02d14043cf072c8297878dd7
diff --git a/src/select.c b/src/select.c
index f0c814b..8e31205 100644
--- a/src/select.c
+++ b/src/select.c
@@ -382,6 +382,7 @@
 
 		rc = osmo_fd_register(ofd);
 		if (rc < 0) {
+			osmo_fd_unregister(ofd);
 			close(ofd->fd);
 			ofd->fd = -1;
 			return rc;