misc: Fix warnings about size of size_t in printf

Fixes warnings like:

warning: format '%d' expects argument of type 'int', but argument 3 has type 'long int' [-Wformat]
diff --git a/openbsc/tests/abis/abis_test.c b/openbsc/tests/abis/abis_test.c
index e7e78d2..53e8a4c 100644
--- a/openbsc/tests/abis/abis_test.c
+++ b/openbsc/tests/abis/abis_test.c
@@ -61,7 +61,7 @@
 	}
 
 	if (descr[0].len != 13) {
-		printf("WRONG SIZE: %d\n", descr[0].len);
+		printf("WRONG SIZE: %zu\n", descr[0].len);
 		abort();
 	}
 
@@ -99,12 +99,12 @@
 	}
 
 	if (descr[0].len != 13) {
-		printf("WRONG SIZE0: %d\n", descr[0].len);
+		printf("WRONG SIZE0: %zu\n", descr[0].len);
 		abort();
 	}
 
 	if (descr[1].len != 13) {
-		printf("WRONG SIZE1: %d\n", descr[1].len);
+		printf("WRONG SIZE1: %zu\n", descr[1].len);
 		abort();
 	}