Fix spelling of 'reasonable' in comments

Signed-off-by: Tom Cosgrove <tom.cosgrove@arm.com>
diff --git a/include/mbedtls/ssl.h b/include/mbedtls/ssl.h
index 610b8b1..328f861 100644
--- a/include/mbedtls/ssl.h
+++ b/include/mbedtls/ssl.h
@@ -4357,7 +4357,7 @@
 void mbedtls_ssl_config_init( mbedtls_ssl_config *conf );
 
 /**
- * \brief          Load reasonnable default SSL configuration values.
+ * \brief          Load reasonable default SSL configuration values.
  *                 (You need to call mbedtls_ssl_config_init() first.)
  *
  * \param conf     SSL configuration context