ssi: xilinx_spips: Skip spi bus update for a few register writes

ssi: xilinx_spips: Skip spi bus update for a few register writes

A few configuration register writes need not update the spi bus state, so just
return after the register write.

Signed-off-by: Sai Pavan Boddu <sai.pavan.boddu@xilinx.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Reviewed-by: Francisco Iglesias <frasse.iglesias@gmail.com>
Tested-by: Francisco Iglesias <frasse.iglesias@gmail.com>
Reviewed-by: Edgar E. Iglesias <edgar.iglesias@xilinx.com>
Message-id: 1573830705-14579-1-git-send-email-sai.pavan.boddu@xilinx.com
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>