drm/i915: fix clear mask in GEN7_MISCCPCTL update

GEN7_DOP_CLOCK_GATE_ENABLE bit should be cleared, not inverse.
The bug was introduced during conversion to intel_uncore_rmw helper.

Suggested-by: Matt Roper <matthew.d.roper@intel.com>
Fixes: 8cee664d ("drm/i915: use proper helper for register updates")
Signed-off-by: Andrzej Hajda <andrzej.hajda@intel.com>
Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>
Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20221017085525.3898649-1-andrzej.hajda@intel.com