serial: imx: disable console clocks on unregister

serial: imx: disable console clocks on unregister

During console setup imx_uart_console_setup() enables clocks, but they
are never disabled when the console is unregistered, this leads to
clk_prepare_enable() being called multiple times without a matching
clk_disable_unprepare() in case of console unregister.

Ensure that clock enable/disable are balanced adding
clk_disable_unprepare() in the console exit callback.

Signed-off-by: Francesco Dolcini <francesco.dolcini@toradex.com>
Link: https://lore.kernel.org/r/20211020192643.476895-3-francesco.dolcini@toradex.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>