ALSA's iec958 plugin by default sets the block start preamble
to 8, whilst this driver was programming the hardware to expect
0xF.
Amend the hardware config to match ALSA.

Signed-off-by: Dave Stevenson <dave.stevenson@raspberrypi.com>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Tested-by: Chanwoo Choi <cw00.choi@samsung.com>
Tested-by: Hoegeun Kwon <hoegeun.kwon@samsung.com>
Tested-by: Stefan Wahren <stefan.wahren@i2se.com>
Link: https://patchwork.freedesktop.org/patch/msgid/d0b126deb228baf1244c91e02ac0a8f7c9c60dc5.1599120059.git-series.maxime@cerno.tech