firmware: fix spi_busy() prototype

Signed-off-by: Jeppe Ledet-Pedersen <jlp@satlab.org>
firmware: mark packet progress fields as volatile

The missing volatile modifier modifier resulted in transmissions without
training sequence if compiled with gcc 4.5. Ouch.

Signed-off-by: Jeppe Ledet-Pedersen <jlp@satlab.org>