[ARM] 4527/1: pxa: fix pxa27x ac97 cold reset in ASoC due to CKEN change

due to CKEN_xxx definition and pxa_set_cken() change,  the pxa27x
ac97 cold reset is broken in ASoC, fixed to use bit index instead
of bit mask

Signed-off-by: eric miao <eric.y.miao@gmail.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>