drm/i915: Add missing ww lock in intel_dsb_prepare.

Because of the long lifetime of the mapping, we cannot wrap this in a
simple limited ww lock. Just use the unlocked version of pin_map,
because we'll likely release the mapping a lot later, in a different
thread.
Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Reviewed-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20210323155059.628690-39-maarten.lankhorst@linux.intel.com

drivers/gpu/drm/i915/display/intel_dsb.c

@@ -293,7 +293,7 @@ void intel_dsb_prepare(struct intel_crtc_state *crtc_state)
 		goto out;
 	}
 
-	buf = i915_gem_object_pin_map(vma->obj, I915_MAP_WC);
+	buf = i915_gem_object_pin_map_unlocked(vma->obj, I915_MAP_WC);
 	if (IS_ERR(buf)) {
 		drm_err(&i915->drm, "Command buffer creation failed\n");
 		i915_vma_unpin_and_release(&vma, I915_VMA_RELEASE_MAP);