clk: imx: Correct the memrepair clock on imx8mp

The root clock slice at offset 0xbf80 should be memrepair
clock, so correct it. And this clock should be always on
to make sure the memory repair function can works well.

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