Fix doxygen for MBEDTLS_SSL_KEYING_MATERIAL_EXPORT

Error was introduced while resolving a merge conflict.

Signed-off-by: Max Fillinger <maximilian.fillinger@foxcrypto.com>
diff --git a/include/mbedtls/mbedtls_config.h b/include/mbedtls/mbedtls_config.h
index df6dacf..d283136 100644
--- a/include/mbedtls/mbedtls_config.h
+++ b/include/mbedtls/mbedtls_config.h
@@ -1764,7 +1764,6 @@
 #define MBEDTLS_SSL_KEEP_PEER_CERTIFICATE
 
 /**
-/*
  * \def MBEDTLS_SSL_KEYING_MATERIAL_EXPORT
  *
  * When this option is enabled, the client and server can extract additional