drm/i915: fix a limit check in hsw_compute_wm_results()

The '!' here was not intended.  Since '!' has higher precedence than
compare, it means the check is never true.

This regression was introduced in

commit 71fff20f
Author: Ville Syrjälä <ville.syrjala@linux.intel.com>
Date:   Tue Aug 6 22:24:03 2013 +0300

    drm/i915: Kill fbc_enable from hsw_lp_wm_results
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_pm.c

@@ -2685,7 +2685,7 @@ static void hsw_compute_wm_results(struct drm_device *dev,
 	 * a WM level. */
 	results->enable_fbc_wm = true;
 	for (level = 1; level <= max_level; level++) {
-		if (!lp_results[level - 1].fbc_val > lp_maximums->fbc) {
+		if (lp_results[level - 1].fbc_val > lp_maximums->fbc) {
 			results->enable_fbc_wm = false;
 			lp_results[level - 1].fbc_val = 0;
 		}