ide-pmac: don't check kauai_lookup_timing() return value

kauai_lookup_timing() should always return non-zero return value:

* BUG() in kauai_lookup_timing() if the timing info cannot be found.

* Remove code checking for zero return value from all callers.

Acked-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Acked-by: Sergei Shtylyov <sshtylyov@ru.mvista.com>
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>