tty: serial: qcom_geni_serial: Allow mctrl when flow control is disabled

The geni set/get_mctrl() functions currently do nothing unless
hardware flow control is enabled. Remove this arbitrary limitation.

Suggested-by: Johan Hovold <johan@kernel.org>
Fixes: 8a8a66a1

 ("tty: serial: qcom_geni_serial: Add support for flow control")
Signed-off-by: Matthias Kaehlcke <mka@chromium.org>
Reviewed-by: Johan Hovold <johan@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>