tty: serial: owl: add "much needed" clk_prepare_enable()

commit 8ba92cf59335 ("arm64: dts: actions: s700: Add Clock Management Unit")
breaks the UART on Cubieboard7-lite (based on S700 SoC), This is due to the
fact that generic clk routine clk_disable_unused() disables the gate clks,
and that in turns disables OWL UART (but UART driver never enables it). To
prove this theory, Andre suggested to use "clk_ignore_unused" in kernel
commnd line and it worked (Kernel happily lands into RAMFS world :)).

This commit fix this up by adding clk_prepare_enable().

Fixes: 8ba92cf59335 ("arm64: dts: actions: s700: Add Clock Management Unit")
Signed-off-by: Amit Singh Tomar <[e-mail]>
Cc: stable <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/tty/serial/owl-uart.c

···
 		return PTR_ERR(owl_port->clk);
 	}
 
+	ret = clk_prepare_enable(owl_port->clk);
+	if (ret) {
+		dev_err(&pdev->dev, "could not enable clk\n");
+		return ret;
+	}
+
 	owl_port->port.dev = &pdev->dev;
 	owl_port->port.line = pdev->id;
 	owl_port->port.type = PORT_OWL;
···
 
 	uart_remove_one_port(&owl_uart_driver, &owl_port->port);
 	owl_uart_ports[pdev->id] = NULL;
+	clk_disable_unprepare(owl_port->clk);
 
 	return 0;
 }