Add logic to wm97xx_read_aux_adc() to retry reading the adc if the
sample failed.  This could occur if the previous sample was still in
the return register or the sample timed-out.  Also avoid a pathologic
failure mode by disabling the digitizer and returning -EBUSY after 5
retries.
Signed-off-by: NEric Millbrandt <emillbrandt@dekaresearch.com>
Acked-by: NMark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: NDmitry Torokhov <dtor@mail.ru>