ssl_tls13_keys.h: use PSA max hash size

Signed-off-by: Przemyslaw Stekiel <przemyslaw.stekiel@mobica.com>
diff --git a/library/ssl_tls13_keys.h b/library/ssl_tls13_keys.h
index b1155fb..d82bf7a 100644
--- a/library/ssl_tls13_keys.h
+++ b/library/ssl_tls13_keys.h
@@ -81,7 +81,7 @@
  * Since contexts are always hashes of message transcripts, this can
  * be approximated from above by the maximum hash size. */
 #define MBEDTLS_SSL_TLS1_3_KEY_SCHEDULE_MAX_CONTEXT_LEN  \
-    MBEDTLS_MD_MAX_SIZE
+    PSA_HASH_MAX_SIZE
 
 /* Maximum desired length for expanded key material generated
  * by HKDF-Expand-Label.