Corrected documentation style

This is for better visuaization with Sphinx

components/nvs_flash/include/nvs_flash.h

@@ -22,6 +22,8 @@ extern "C" {
 
     Temporarily, this region is hardcoded as a 12KB (0x3000 byte)
     region starting at 24KB (0x6000 byte) offset in flash.
+
+    @return ESP_OK if flash was successfully initialised.
 */
 esp_err_t nvs_flash_init(void);