clk: imx8mp: Remove non-existent IMX8MP_CLK_AUDIOMIX_PDM_ROOT

The TRM shows there is only one AUDIOMIX PDM Root Clock Select
register, and it's called IMX8MP_CLK_AUDIOMIX_PDM_SEL.  That
selector doesn't appear to have any more children and the
MICFIL driver can reference IMX8MP_CLK_AUDIOMIX_PDM_SEL
directly without the need for any other.  Remove this
errant clock, since it doesn't really exist.

Signed-off-by: Adam Ford <aford173@gmail.com>
Acked-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20230831044431.250338-3-aford173@gmail.com
Signed-off-by: Abel Vesa <abel.vesa@linaro.org>

Author: aford173

include/dt-bindings/clock/imx8mp-clock.h

@@ -376,7 +376,6 @@
 #define IMX8MP_CLK_AUDIOMIX_MU2_ROOT		36
 #define IMX8MP_CLK_AUDIOMIX_MU3_ROOT		37
 #define IMX8MP_CLK_AUDIOMIX_EARC_PHY		38
-#define IMX8MP_CLK_AUDIOMIX_PDM_ROOT		39
 #define IMX8MP_CLK_AUDIOMIX_SAI1_MCLK1_SEL	40
 #define IMX8MP_CLK_AUDIOMIX_SAI1_MCLK2_SEL	41
 #define IMX8MP_CLK_AUDIOMIX_SAI2_MCLK1_SEL	42