ARM: dts: imx6qdl-colibri: Mux mclk for sgtl5000 with the codec node

Move the pin muxing for MCLK used by the codec to the codec node
instead of placing it inside the audmux pinctrl group.

While no negative effects have been observed this should make sure that
MCLK is provided when the codec driver is probed.

Follows commit fa51e1dc ("ARM: dts: imx6qdl-apalis: Fix sgtl5000
detection issue")

Reviewed-by: Fabio Estevam <festevam@gmail.com>
Signed-off-by: Max Krummenacher <max.krummenacher@toradex.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>