drm/i915: kill dev_priv->mchdev_lock

It's only ever a pointer to the global mchdev_lock, and we don't use
it at all.
Reviewed-by: NDamien Lespiau <damien.lespiau@intel.com>
Reviewed-by: NChris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_drv.h

@@ -850,7 +850,6 @@ typedef struct drm_i915_private {
 	int c_m;
 	int r_t;
 	u8 corr;
-	spinlock_t *mchdev_lock;
 
 	enum no_fbc_reason no_fbc_reason;
 

drivers/gpu/drm/i915/intel_pm.c

@@ -3188,7 +3188,6 @@ void intel_gpu_ips_init(struct drm_i915_private *dev_priv)
 	 * set up, to avoid intel-ips sneaking in and reading bogus values. */
 	spin_lock(&mchdev_lock);
 	i915_mch_dev = dev_priv;
-	dev_priv->mchdev_lock = &mchdev_lock;
 	spin_unlock(&mchdev_lock);
 
 	ips_ping_for_i915_load();