ASoC: atmel-i2s: do not warn if muxclk is missing

ASoC: atmel-i2s: do not warn if muxclk is missing

Besides the fact that muxclk is optional, muxclk can be set using
assigned-clocks, removing the need to set it in driver. The warning is
thus unneeded, so we can transform it in a debug print, eventually to just
reflect that muxclk was not set by the driver.

Signed-off-by: Codrin Ciubotariu <codrin.ciubotariu@microchip.com>
Link: https://lore.kernel.org/r/20201103100554.1307190-1-codrin.ciubotariu@microchip.com
Signed-off-by: Mark Brown <broonie@kernel.org>