serial: ar933x_uart: disable clk on error handling path in probe

ar933x_uart_probe() does not invoke clk_disable_unprepare()
on one error handling path. This patch fixes that.

Fixes: 9be1064f

 ("serial: ar933x_uart: add RS485 support")
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>
Link: https://lore.kernel.org/r/20201111124426.42638-1-zhengzengkai@huawei.com
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>