wifi: wfx: Remove some dead code

wait_for_completion_timeout() can not return a <0 value.
So simplify the logic and remove dead code.

-ERESTARTSYS can not be returned by do_wait_for_common() for tasks with
TASK_UNINTERRUPTIBLE, which is the case for wait_for_completion_timeout()

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Reviewed-by: Jérôme Pouiller <jerome.pouiller@silabs.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/809c4a645c8d1306c0d256345515865c40ec731c.1676464422.git.christophe.jaillet@wanadoo.fr