duo/spi.c: fix memory leak issue.
duo/spi.c: fix memory leak issue.

ganshun666/micropython,redbear/micropython,redbear/micropython,ganshun666/micropython,ganshun666/micropython,redbear/micropython,ganshun666/micropython,redbear/micropython,redbear/micropython,ganshun666/micropython