ALSA: Fix pxa2xx-ac97-lib.c compilation

The last ALSA merge broke pxa2xx-ac97-lib.c, as it brought back
references to cpu_is_pxa21x that Eric Miao removed in commit
0ffcbfd54ea81ca24c0749f55ca4fcf3e2bdc23e:

	[ARM] pxa: make cpu_is_pxa2* macros more consistent

This patch gets rid of those references, and only keeps cpu_is_pxa25x().

Signed-off-by: Marc Zyngier <maz@misterjones.org>
Acked-by: Eric Miao <eric.miao@marvell.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>