tty: serial: qcom-geni-serial: Implement start_rx callback

In suspend sequence stop_rx will be performed only if implementation for
start_rx callback is present.

Set qcom_geni_serial_start_rx as callback for start_rx so that stop_rx is
performed.

Fixes: c9d2325c

 ("serial: core: Do stop_rx in suspend path for console if console_suspend is disabled")
Reviewed-by: Douglas Anderson <dianders@chromium.org>
Signed-off-by: Vijaya Krishna Nivarthi <quic_vnivarth@quicinc.com>
Link: https://lore.kernel.org/r/1654627965-1461-3-git-send-email-quic_vnivarth@quicinc.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>