clk: clk-imx7d: fix ahb clk definition

MX7D ahb clk actually has no LPCG gate, current LPCG offset 0x4200
used actually is for adc, not ahb. After fix, correct ocram_s_clk
parent accordingly as well.

Cc: Shawn Guo <shawnguo@kernel.org>
Cc: Fabio Estevam <fabio.estevam@nxp.com>
Reviewed-by: Stefan Agner <stefan@agner.ch>
Tested-by: Stefan Agner <stefan@agner.ch>
Signed-off-by: Dong Aisheng <aisheng.dong@nxp.com>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>