ALSA: pxa27x: rename pxa27x_assert_ac97reset()

This patch does nothing functionally, it just gives the function a new name and
modifies the prototype slightly in order to clarify what the function is doing
(which is not necessarily asserting the reset).
Some commentary also added.

Tested on a palm treo 680 machine.

Signed-off-by: Mike Dunn <mikedunn@newsguy.com>
Acked-by: Igor Grinberg <grinberg@compulab.co.il>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>