clk: imx8mp: Fix the parent clk of the audio_root_clk

clk: imx8mp: Fix the parent clk of the audio_root_clk

Having the parent of the audio_root_clk set to ipg_root
in the clk-imx8mp.c, there is a hang happening when the
audiomix IP regs are accessed. Switch parent to audio_ahb.

And we could also refer to the section "5.1.4 System Clocks" of the
IMX8MPRM.pdf, the parent clk of CCGR101 (Audiomix) is the
AUDIO_AHB_CLK_ROOT.

Signed-off-by: Hui Wang <hui.wang@canonical.com>
Reviewed-by: Abel Vesa <abel.vesa@nxp.com>
Link: https://lore.kernel.org/r/20211109125657.63485-2-hui.wang@canonical.com
Signed-off-by: Abel Vesa <abel.vesa@nxp.com>