libhfuzz: fix HF_strlcpy so it matches the strlcpy spec (ret value)

libhfuzz/memorycmp.c

diff --git a/libhfuzz/memorycmp.c b/libhfuzz/memorycmp.c
index 8f912c0..90b91f5 100644
--- a/libhfuzz/memorycmp.c
+++ b/libhfuzz/memorycmp.c
@@ -221,7 +221,7 @@
     }
 
     dest[len] = '\0';
-    return len;
+    return slen;
 }
 
 static inline size_t HF_strlcat(char* dest, const char* src, size_t sz, uintptr_t addr) {