clk: imx7d: correct dram pll type

DRAM PLL is a audio/video type PLL, need to correct
it to get correct ops of PLL.

Signed-off-by: Anson Huang <b20788@freescale.com>
Signed-off-by: Dong Aisheng <aisheng.dong@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>