Changes

scheduler: trx_sched_is_sacch_fn(): fix returning non-bool

The function is declared `bool` but returns `-EINVAL` on an error path.
`-EINVAL` is `-22`, which in C implicitly converts to `bool true`.
Returning `false` makes more sense when we don't know the MF layout.

Change-Id: Ib2394687815aed4990c3880446176e4c97440667