uhidev(9): Partially fix uhidev_write aborting.

In my previous change, I intended to make uhidev_stop abort any
pending write -- but I forgot to initialize sc->sc_writereportid, so
it never did anything.

This changes the API and ABI of uhidev_write so it takes the struct
uhidev pointer, rather than the struct uhidev_softc pointer; this way
uhidev_write knows what the report id of the client is, so it can
arrange to have uhidev_stop abort only this one.

XXX Except it still doesn't actually work because we do this
unlocked, ugh, so the write might complete before we abort anything.
To be fixed some more in a later change.

XXX kernel ABI change to uhidev_write signature, used by uhidev
driver modules, requires bump

(riastradh)