Address comments in psk client review

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Refine cipher suite related code in psk
Refine get_psk_offered()

Change-Id: Ic3b0b5f86eb1e71f11bb499961aa8494284f1840
Signed-off-by: XiaokangQian <xiaokang.qian@arm.com>
diff --git a/library/ssl_client.c b/library/ssl_client.c
index 5e775cc..8e4e968 100644
--- a/library/ssl_client.c
+++ b/library/ssl_client.c
@@ -653,7 +653,7 @@
             return( ret );
         p += output_len;
     }
-#endif /* MBEDTLS_SSL_PROTO_TLS1_3 || MBEDTLS_KEY_EXCHANGE_SOME_PSK_ENABLED */
+#endif /* MBEDTLS_SSL_PROTO_TLS1_3 && MBEDTLS_KEY_EXCHANGE_SOME_PSK_ENABLED */
 
     /* Write the length of the list of extensions. */
     extensions_len = p - p_extensions_len - 2;