Fix typo in doc'n of session resumption API

Signed-off-by: Hanno Becker <hanno.becker@arm.com>
diff --git a/include/mbedtls/ssl.h b/include/mbedtls/ssl.h
index 1e8976e..68fee03 100644
--- a/include/mbedtls/ssl.h
+++ b/include/mbedtls/ssl.h
@@ -3718,7 +3718,7 @@
  *                 This must have been initialized with mbedtls_ssl_init_session()
  *                 but otherwise be unused.
  *
- * \note           This function can handle a variety of mechanism for session
+ * \note           This function can handle a variety of mechanisms for session
  *                 resumption: For TLS 1.2, both session ID-based resumption and
  *                 ticket-based resumption will be considered. For TLS 1.3,
  *                 once implemented, sessions equate to tickets, and calling