Move the WARN_ON() into the if condition so the compiler can see that
the branch is unlikely() and possibly optimize it better.

Cc: Maulik Shah <mkshah@codeaurora.org>
Reviewed-by: Douglas Anderson <dianders@chromium.org>
Reviewed-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Signed-off-by: Stephen Boyd <swboyd@chromium.org>
Link: https://lore.kernel.org/r/20200521060425.24285-4-swboyd@chromium.orgSigned-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>