arm64: dts: imx8: fix audio lpcg index

arm64: dts: imx8: fix audio lpcg index

lpcg cell0 should be clock's 'indices' instead of 'index'.

imx_lpcg_of_clk_src_get(struct of_phandle_args *clkspec, void *data)
{
        struct clk_hw_onecell_data *hw_data = data;
        unsigned int idx = clkspec->args[0] / 4;

	....
}

<@sai0_lpcg 1> will be the same as <@sai_lpcg 0>.

Replace 0 with IMX_LPCG_CLK_0 and replace 1 with IMX_LPCG_CLK_4.

It can work at iMX8QXP because IMX_LPCG_CLK_4 is ipg clock, which already
enabled. But for iMX8QM IMX_LPCG_CLK_4 is mclk, which trigger issue.

Fixes: 0a9279e9ae88 ("arm64: dts: imx8qxp: Add audio SAI nodes")
Signed-off-by: Frank Li <Frank.Li@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>