idr: make ida_simple_remove() return an error

idr: make ida_simple_remove() return an error

The idr interface is pretty horrible, in that it doesn't return an
error if we attempt to free an invalid ID, instead it calls
WARN(). That's not great if we're potentially exposing this as a
user visible interface, indirectly.

So add __ida_remove() that returns an error instead of warning,
and change ida_simple_remove() to use that interface. Alternatively
we could make ida_remove() return an error, but then I'd have to
verify all call sites...

Signed-off-by: Jens Axboe <axboe@fb.com>