psa: Fix the size of hash buffers

Fix the size of hash buffers for PSA hash
operations.

Signed-off-by: Ronald Cron <ronald.cron@arm.com>
diff --git a/library/ssl_srv.c b/library/ssl_srv.c
index 5e2d152..f34f2de 100644
--- a/library/ssl_srv.c
+++ b/library/ssl_srv.c
@@ -3098,7 +3098,11 @@
     {
         size_t dig_signed_len = ssl->out_msg + ssl->out_msglen - dig_signed;
         size_t hashlen = 0;
+#if defined(MBEDTLS_USE_PSA_CRYPTO)
+        unsigned char hash[PSA_HASH_MAX_SIZE];
+#else
         unsigned char hash[MBEDTLS_MD_MAX_SIZE];
+#endif
         int ret = MBEDTLS_ERR_ERROR_CORRUPTION_DETECTED;
 
         /*