ASoC: rockchip: i2s-tdm: Remove call to rockchip_i2s_ch_to_io

The call to rockchip_i2s_ch_to_io is only useful for its return
value which is not being used. The function call also has no
side effects, the call is effectively useless and can be removed.

Addresses-Coverity: ("Useless call")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Message-Id: <20211008095430.62680-1-colin.king@canonical.com>
Signed-off-by: Mark Brown <broonie@kernel.org>