drm/i915: s/pm_intr_keep/pm_intrmsk_mbz

"pm_intr_keep" is not conveying the intent that it is bitmask
of interrupts that must be zero(mbz) in GEN6_PMINTRMSK.
Name it "pm_intrmsk_mbz".

Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Radoslaw Szwichtenberg <radoslaw.szwichtenberg@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Sagar Arun Kamble <sagar.a.kamble@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1489199821-6707-2-git-send-email-sagar.a.kamble@intel.com
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index 4d1fb62..f4d87d3 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -1337,7 +1337,7 @@ struct intel_gen6_power_mgmt {
 	u32 pm_iir;
 
 	/* PM interrupt bits that should never be masked */
-	u32 pm_intr_keep;
+	u32 pm_intrmsk_mbz;
 
 	/* Frequencies are stored in potentially platform dependent multiples.
 	 * In other words, *_freq needs to be multiplied by X to be interesting.