serial: 8250_uniphier: call clk_disable_unprepare() on failure path

If serial8250_register_8250_port() fails, disable and unprepare the
clock before exiting.

Fixes: 1a8d2903 ("serial: 8250_uniphier: add UniPhier serial driver")
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Reviewed-by: Matthias Brugger <matthias.bgg@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>