[ALSA] ppc32: Fix Alsa PowerMac driver on old machines

PPC PMAC driver
The g5 support code broke some earlier models unfortunately as those
bail out early from the detect function, before the point where I added
the code to locate the PCI device for use with DMA allocations.

This patch fixes it.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>