clk: imx: Remove __init for imx_register_uart_clocks() API

Some of i.MX SoCs' clock driver use platform driver model,
and they need to call imx_register_uart_clocks() API, so
imx_register_uart_clocks() API should NOT be in .init section.

Signed-off-by: Anson Huang <Anson.Huang@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>