Corrected misleading fn description in ssl_cache.h

Mistake in comments spotted by Andris Mednis
diff --git a/include/polarssl/ssl_cache.h b/include/polarssl/ssl_cache.h
index 063d7d7..9e77861 100644
--- a/include/polarssl/ssl_cache.h
+++ b/include/polarssl/ssl_cache.h
@@ -122,7 +122,7 @@
 #endif /* POLARSSL_HAVE_TIME */
 
 /**
- * \brief          Set the cache timeout
+ * \brief          Set the maximun number of cache entries
  *                 (Default: SSL_CACHE_DEFAULT_MAX_ENTRIES (50))
  *
  * \param cache    SSL cache context