Use the correct variable when tracking padding length

Fixes an error introduced in a81373f80

Signed-off-by: Tom Cosgrove <tom.cosgrove@arm.com>
diff --git a/library/ssl_msg.c b/library/ssl_msg.c
index c8ffc1e..85632a1 100644
--- a/library/ssl_msg.c
+++ b/library/ssl_msg.c
@@ -1973,7 +1973,7 @@
             increment = mbedtls_ct_size_if_else_0(b, increment);
             pad_count += increment;
         }
-        correct = mbedtls_ct_size_if_else_0(mbedtls_ct_uint_eq(pad_count, padlen), padlen);
+        correct = mbedtls_ct_size_if_else_0(mbedtls_ct_uint_eq(pad_count, padlen), correct);
 
 #if defined(MBEDTLS_SSL_DEBUG_ALL)
         if (padlen > 0 && correct == 0) {