Corrected misleading fn description in ssl_cache.h

Mistake in comments spotted by Andris Mednis
diff --git a/include/mbedtls/ssl_cache.h b/include/mbedtls/ssl_cache.h
index 53f043e..18ec16a 100644
--- a/include/mbedtls/ssl_cache.h
+++ b/include/mbedtls/ssl_cache.h
@@ -121,7 +121,7 @@
 #endif /* MBEDTLS_HAVE_TIME */
 
 /**
- * \brief          Set the cache timeout
+ * \brief          Set the maximun number of cache entries
  *                 (Default: MBEDTLS_SSL_CACHE_DEFAULT_MAX_ENTRIES (50))
  *
  * \param cache    SSL cache context