arm64: dts: freescale: imx8mm-verdin-dahlia: add Microphone Jack to sound card

The simple-audio-card's microphone widget currently connects to the
headphone jack. Routing the microphone input to the microphone jack
allows for independent operation of the microphone and headphones.

This resolves the following boot-time kernel log message, which
indicated a conflict when the microphone and headphone functions were
not separated:
  debugfs: File 'Headphone Jack' in directory 'dapm' already present!

Fixes: 6a57f224 ("arm64: dts: freescale: add initial support for verdin imx8m mini")
Signed-off-by: Stefan Eichenberger <stefan.eichenberger@toradex.com>
Reviewed-by: Francesco Dolcini <francesco.dolcini@toradex.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>