drm/gf119-/disp: fix nasty bug which can clobber SOR0's clock setup

commit 0f1d360b2ee3a2a0f510d3f1bcd3f5ebe5d41265 upstream.

Fixes a LVDS bleed issue on Lenovo W530 that can occur under a
number of circumstances.

Signed-off-by: Ben Skeggs <bskeggs@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>