ipa: Fix the size of the streamid array used in the proxy code

We want to store stream ids 0 to 0xff. This means we need to have
256 entries in this array.

Fixes: Coverity CID 1040697, CID 1040696, CID 1040695, CID 1040694
diff --git a/src/ipa_proxy.c b/src/ipa_proxy.c
index 9816d02..ad6e1b5 100644
--- a/src/ipa_proxy.c
+++ b/src/ipa_proxy.c
@@ -67,13 +67,13 @@
 		struct ipa_proxy_instance	*inst;
 		struct bitvec			streamid_map;
 		uint8_t				streamid_map_data[(0xff+1)/8];
-		uint8_t				streamid[0xff];
+		uint8_t				streamid[0xff + 1];
 	} src;
 	struct {
 		struct ipa_proxy_instance	*inst;
 		struct bitvec			streamid_map;
 		uint8_t				streamid_map_data[(0xff+1)/8];
-		uint8_t				streamid[0xff];
+		uint8_t				streamid[0xff + 1];
 	} dst;
 
 	struct llist_head			conn_list;