serial: st-asc: Use generic DT binding for announcing RTS/CTS lines

The initial binding 'st,hw-flow-control' isn't used anywhere, in neither
in upstream nor downstream kernels.  It isn't even documented in
dt-bindings, so we can safely assume it's safe to swap to the generic
one.
Acked-by: Peter Griffin <peter.griffin@linaro.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/st-asc.c

@@ -794,7 +794,7 @@ static struct asc_port *asc_of_get_asc_port(struct platform_device *pdev)
 		return NULL;
 
 	asc_ports[id].hw_flow_control = of_property_read_bool(np,
-							"st,hw-flow-control");
+							"uart-has-rtscts");
 	asc_ports[id].force_m1 =  of_property_read_bool(np, "st,force_m1");
 	asc_ports[id].port.line = id;
 	asc_ports[id].rts = NULL;