drm/i915: fix CB tuning check for ILK+

drm/i915: fix CB tuning check for ILK+

commit cb0e093162d7b6589c2217a00e2abfef686b32d6 upstream.

CB tuning is needed to handle potential process variations that might
cause clock jitter for certain PLL settings.  However, we were setting
it incorrectly since we were using the wrong M value as a check (M1 when
we needed to use the whole M value).  Fix it up, making my HDMI
attached display a little prettier (used to have occasional dots crawl
across the display).

Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: Keith Packard <keithp@keithp.com>
Signed-off-by: Timo Aaltonen <timo@canonical.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>