tty: serial: qcom_geni_serial: Use iowrite32_rep to write to FIFO

Use iowrite32_rep to write to the hardware FIFO so that the code does
not have to worry about the system endianness.

Signed-off-by: Karthikeyan Ramasubramanian <kramasub@codeaurora.org>
Reviewed-by: Matthias Kaehlcke <mka@chromium.org>
Reviewed-by: Stephen Boyd <swboyd@chromium.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>