ALSA: ppc: keywest: check if DEQ was already instantiated

Due to changes in i2c-powermac, for some Macs the DEQ is instantiated
now in i2c-powermac while some need the instantiation here in the
keywest sound driver. The proper fix is to convert this driver to AOA.
Until then support both ways of instantiation. Before this patch, some
Macs lost sound because the sound driver failed when instantiating the
DEQ for the second time.

Signed-off-by: Wolfram Sang <wsa@the-dreams.de>
Tested-by: Dan DeVoto <dand1972@yahoo.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>