ASoC: sun4i-i2s: Fix lrck_period computation for I2S justified mode

Left and Right justified mode are computed using the same formula
as DSP_A and DSP_B mode.
Which is wrong and the user manual explicitly says:

LRCK_PERDIOD:
PCM Mode: Number of BCLKs within (Left + Right) channel width.
I2S/Left-Justified/Right-Justified Mode: Number of BCLKs within each
individual channel width(Left or Right)

Fix this by using the same formula as the I2S mode.

Fixes: 7ae7834e

 ("ASoC: sun4i-i2s: Add support for DSP formats")
Signed-off-by: Clément Péron <peron.clem@gmail.com>
Acked-by: Maxime Ripard <mripard@kernel.org>
Link: https://lore.kernel.org/r/20201030144648.397824-2-peron.clem@gmail.com
Signed-off-by: Mark Brown <broonie@kernel.org>