call Spark.process() when OTA_FLASH has started, regardless of mode. 

Tested:

- Flashed via usb a modified tinker app with mode MANUAL, and Spark.connect() in setup, Spark.process() in loop, and this fix in place. 
- Loaded the same app into the inline IDE. Successfully performed OTA flash (verifying the fix)
- Attempted to flash again (now that the firmware in the core is build in the cloud without the fix), get the stuck magenta followed by reset few seconds later.