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 <[e-mail]>
Acked-by: Rob Herring <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Abel Vesa <[e-mail]>

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

···
 #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