arm64: dts: imx8mp: correct sdhc ipg clk

[ Upstream commit eab6ba2a ]

The ipg clk for sdhc sources from IPG_CLK_ROOT per i.MX 8M Plus
Applications Processor Reference Manual, Table 5-2. System Clocks.

Fixes: 6d9b8d20 ("arm64: dts: freescale: Add i.MX8MP dtsi support")
Signed-off-by: Peng Fan <peng.fan@nxp.com>
Reviewed-by: Fabio Estevam <festevam@gmail.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>