tty: serial: qcom-geni-serial: stop operations in progress at shutdown

We don't stop transmissions in progress at shutdown. This is fine with
FIFO SE mode but with DMA (support for which we'll introduce later) it
causes trouble so fix it now.

Fixes: e8376633

 ("tty: serial: qcom_geni_serial: No need to stop tx/rx on UART shutdown")
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
Reviewed-by: Konrad Dybcio <konrad.dybcio@linaro.org>
Link: https://lore.kernel.org/r/20221229155030.418800-2-brgl@bgdev.pl
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>