logging: Replace remaining fprintf() calls with libosmocore logging

Change-Id: I2a772b3180131923d4e2ee7311670b938cb50fe0
diff --git a/src/client/remsim_client_main.c b/src/client/remsim_client_main.c
index f064960..47ec8ac 100644
--- a/src/client/remsim_client_main.c
+++ b/src/client/remsim_client_main.c
@@ -188,7 +188,7 @@
 
 	/* Silently (and portably) reap children. */
 	if (avoid_zombies() < 0) {
-		fprintf(stderr, "Unable to silently reap children: %s\n", strerror(errno));
+		LOGP(DMAIN, LOGL_FATAL, "Unable to silently reap children: %s\n", strerror(errno));
 		exit(1);
 	}