Remove the cmd_timed and cmd_timed_errno members from the internal
struct subdevice_struct.
cmd_timed_errno is checked but never set, so it will always be 0 and the
code that uses it is buggy as it returns the value of s->cmd_mask_errno
if s->cmd_timed_errno is non-zero and sets s->cmd_mask_errno on failure.
It shouldn't be setting s->cmd_mask_errno at all.
Since the generic timed command could depend on the length of the
channel list, don't bother caching the result, and don't set
s->cmd_mask_errno on failure.
0868eccbf7