bsc: fix bail out in case of problems bootstrapping BTS or E1 input

The error message was missing in case of problems bootstrapping the BTS.
The E1 input driver initialization was displayed in the standard output,
now this error is reported via logs.
diff --git a/openbsc/src/libbsc/bsc_init.c b/openbsc/src/libbsc/bsc_init.c
index c173c62..ecb4e44 100644
--- a/openbsc/src/libbsc/bsc_init.c
+++ b/openbsc/src/libbsc/bsc_init.c
@@ -439,7 +439,10 @@
 
 	llist_for_each_entry(bts, &bsc_gsmnet->bts_list, list) {
 		rc = bootstrap_bts(bts);
-
+		if (rc < 0) {
+			LOGP(DNM, LOGL_FATAL, "Error bootstrapping BTS\n");
+			return rc;
+		}
 		switch (bts->type) {
 		case GSM_BTS_TYPE_NANOBTS:
 		case GSM_BTS_TYPE_HSL_FEMTO:
@@ -448,10 +451,9 @@
 			rc = e1_reconfig_bts(bts);
 			break;
 		}
-
 		if (rc < 0) {
-			fprintf(stderr, "Error in E1 input driver setup\n");
-			exit (1);
+			LOGP(DNM, LOGL_FATAL, "Error enabling E1 input driver\n");
+			return rc;
 		}
 	}