ASoC: SOF: fix race in FW boot timeout handling

A race condition exists in handling firmware boot timeout.
If FW sends FW_READY just after boot timeout has expired in
driver, a kernel exception will result as FW_READY handler
will be run while the state is still being cleaned up in
snd_sof_run_firmware(). Avoid the race by setting
boot_complete also in the error case.

Signed-off-by: Kai Vehmanen <kai.vehmanen@linux.intel.com>
Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Signed-off-by: Mark Brown <broonie@kernel.org>