correctly use asn1c API: PDU pointers must be NULL when calling decoder

If the pointers are != NULL, asn1c assumes their memory has already been
allocated, rather than dynamically allocating storage for it.

Change-Id: I6b78be75d8927f032ca4051520a3053b3fbf9e13
diff --git a/src/rspro_util.c b/src/rspro_util.c
index 79c7c03..82adb88 100644
--- a/src/rspro_util.c
+++ b/src/rspro_util.c
@@ -51,7 +51,7 @@
 /* consumes 'msg' _if_ it is successful */
 RsproPDU_t *rspro_dec_msg(struct msgb *msg)
 {
-	RsproPDU_t *pdu;
+	RsproPDU_t *pdu = NULL;
 	asn_dec_rval_t rval;
 
 	printf("decoding %s\n", msgb_hexdump(msg));