drm: kirin960: Revert change that broke a number of modes

After adding missing modelines in the adv7511 hack, I
found 4.14+ kernels were still having trouble generating
the right frequencies to get sane display.

After looking through the differences between 4.9 and 4.14,
I found the following change which causes the issue.

This patch undoes that problematic change

Signed-off-by: John Stultz <john.stultz@linaro.org>
Change-Id: I3fbe2fb4c51d50bc27da007ba6c4d49122205b57
1 file changed