MFIB: coverity fixes

Change-Id: I5c1bc498f7299e175070eb288e40f8d037c9be3a
Signed-off-by: Neale Ranns <nranns@cisco.com>
diff --git a/src/vnet/mfib/ip6_mfib.c b/src/vnet/mfib/ip6_mfib.c
index d47887b..aa9fdb9 100644
--- a/src/vnet/mfib/ip6_mfib.c
+++ b/src/vnet/mfib/ip6_mfib.c
@@ -438,7 +438,7 @@
     {
 	len = table->prefix_lengths_in_search_order[i];
 
-	ASSERT(len >= 0 && len <= 256);
+	ASSERT(len <= 256);
         IP6_MFIB_MK_KEY(mfib, grp, src, len, key);
 
 	rv = clib_bihash_search_inline_2_40_8(&table->ip6_mhash, &key, &value);