Add missing include

Fix build failures with config full

Signed-off-by: Manuel Pégourié-Gonnard <manuel.pegourie-gonnard@arm.com>
diff --git a/library/ssl_tls13_client.c b/library/ssl_tls13_client.c
index 48780d8..3dffc1d 100644
--- a/library/ssl_tls13_client.c
+++ b/library/ssl_tls13_client.c
@@ -33,6 +33,7 @@
 #include "ssl_client.h"
 #include "ssl_tls13_keys.h"
 #include "ssl_debug_helpers.h"
+#include "md_psa.h"
 
 #define PSA_TO_MBEDTLS_ERR(status) PSA_TO_MBEDTLS_ERR_LIST(status,   \
                                                            psa_to_ssl_errors,             \