ASoC: pcm512x: revert downstream changes

This partially reverts commit 185ea054
which was added by https://github.com/raspberrypi/linux/pull/1152



The downstream pcm512x changes caused a regression, it broke normal
use of the 24bit format with the codec, eg when using simple-audio-card.

The actual bug with 24bit playback is the incorrect usage
of physical_width in various drivers in the downstream tree
which causes 24bit data to be transmitted with 32 clock
cycles. So it's not the pcm512x that needs fixing, it's the
soundcard drivers.

Signed-off-by: Matthias Reichl <hias@horus.com>