Fix index in the loop of uw_crypto_utils_equal_

Change-Id: I0021d535eaaa08c239649f36ffa353b22844f905
Reviewed-on: https://weave-review.googlesource.com/1944
Reviewed-by: Alex Vakulenko <avakulenko@google.com>

third_party/libuweave/src/crypto_utils.c

diff --git a/third_party/libuweave/src/crypto_utils.c b/third_party/libuweave/src/crypto_utils.c
index 75bd2e5..76b8068 100644
--- a/third_party/libuweave/src/crypto_utils.c
+++ b/third_party/libuweave/src/crypto_utils.c
@@ -16,7 +16,7 @@
 
   uint8_t diff = 0;
   for (size_t i = 0; i < len; i++) {
-    diff |= arr1[0] ^ arr2[0];
+    diff |= arr1[i] ^ arr2[i];
   }
 
   return 0 == diff;