firmware: thead,th1520-aon: Fix use after free in th1520_aon_init()

Record the error code before freeing "aon_chan" to avoid a
use after free.

Fixes: e4b3cbd8 ("firmware: thead: Add AON firmware protocol driver")
Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
Link: https://lore.kernel.org/r/f19be994-d355-48a6-ab45-d0f7e5955daf@stanley.mountain


Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>