drm/bridge: dw-hdmi-i2s: reset audio fifo before applying new params

When changing the audio hw params, reset the audio fifo to make sure
any old remaining data is flushed.

The databook mentions that such reset should be followed by a reset of
the i2s block to make sure the samples stay aligned

Reviewed-by: Jonas Karlman <jonas@kwiboo.se>
Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>
Reviewed-by: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190812120726.1528-7-jbrunet@baylibre.com