Fix incrementing pointer instead of value

This was introduced by a hasty search-and-replace that didn't account for C's
operator precedence when changing those variables to pointer types.
diff --git a/ChangeLog b/ChangeLog
index b8dc65c..ef2e7b7 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,15 @@
 mbed TLS ChangeLog (Sorted per branch, date)
 
+= mbed TLS 2.16.5 branch released xxxx-xx-xx
+
+Security
+   * Fix potential memory overread when performing an ECDSA signature
+     operation. The overread only happens with cryptographically low
+     probability (of the order of 2^-n where n is the bitsize of the curve)
+     unless the RNG is broken, and could result in information disclosure or
+     denial of service (application crash or extra resource consumption).
+     Reported by Peter and Auke (found using static analysis).
+
 = mbed TLS 2.16.4 branch released 2020-01-15
 
 Security