drm/panel: Fix ARM Versatile panel clocks

These clocks are in kHz not in Hz, oops. Fix it so my
new bandwidth calculations patch starts working with these
panels.

Reviewed-by: Eric Anholt <eric@anholt.net>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20180211103840.18764-1-linus.walleij@linaro.org