clk: imx8mn: fix int pll clk gate

To Frac pll, the gate shift is 13, however to Int PLL the gate shift
is 11.

Signed-off-by: Peng Fan <peng.fan@nxp.com>
Reviewed-by: Jacky Bai <ping.bai@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>