serial: sccnxp: Use devm_clk_get_enabled() helper

The devm_clk_get_enabled() helper:
   - calls devm_clk_get()
   - calls clk_prepare_enable() and registers what is needed in order to
     call clk_disable_unprepare() when needed, as a managed resource.

This simplifies the code.
This also avoids some other warnings/issues. (see [1])

[1]: https://lore.kernel.org/all/20221118233101.never.215-kees@kernel.org/

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Link: https://lore.kernel.org/r/735a807c2df835aa436dcbc76b374f983f89a9af.1672419577.git.christophe.jaillet@wanadoo.fr
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>