ASoC: mediatek: Remove unused mtk_memif_set_rate

mtk_memif_set_rate() has been unused since it was added in the 2019
commit 9cdf85a1 ("ASoC: mediatek: common: add some helpers to control
mtk_memif")

Remove it.

(The _substream version is used, and is left in)

Signed-off-by: Dr. David Alan Gilbert <linux@treblig.org>
Link: https://patch.msgid.link/20250201005021.447726-1-linux@treblig.org


Signed-off-by: Mark Brown <broonie@kernel.org>