drm/i915: Use a mask when applying WaProgramL3SqcReg1Default

Otherwise we are blasting other bits in GEN8_L3SQCREG1 that might be important
(although we probably aren't at the moment because 0 seems to be the default
for all the other bits).

v2: Extra parentheses (Michel)

Fixes: 050fc465 ("drm/i915:bxt: implement WaProgramL3SqcReg1DefaultForPerf")
Fixes: 450174fe ("drm/i915/chv: Tune L3 SQC credits based on actual latencies")
Signed-off-by: Oscar Mateo <oscar.mateo@intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Imre Deak <imre.deak@intel.com>
Reviewed-by: Michel Thierry <michel.thierry@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/1508271945-14961-1-git-send-email-oscar.mateo@intel.com


Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>