spi: spi-geni-qcom: Combine the clock setting code

There is code for adjusting the clock both in setup_fifo_params()
(called from prepare_message()) and in setup_fifo_xfer() (called from
transfer_one()).  The code is the same.  Abstract it out to a shared
function.

This is a no-op cleanup patch.  The only change is to the error string
if we fail to set the clock.  Since the two paths has marginally
different error messages I picked the clean one.

Acked-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Douglas Anderson <dianders@chromium.org>
Signed-off-by: Akash Asthana <akashast@codeaurora.org>
Link: https://lore.kernel.org/r/1592908737-7068-6-git-send-email-akashast@codeaurora.org
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>