drm/i915: Don't leak the capture list items

When we recently converted the capture code to use vma snapshots,
we forgot to free the struct i915_capture_list list items after use.

Fix that by bringing back a kfree.

Fixes: ff20afc4ce ("drm/i915: Update error capture code to avoid using the current vma state")
Cc: Ramalingam C <ramalingam.c@intel.com>
Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20211209141304.393479-1-thomas.hellstrom@linux.intel.com

drivers/gpu/drm/i915/i915_request.c

@@ -307,6 +307,7 @@ void i915_request_free_capture_list(struct i915_capture_list *capture)
 		struct i915_capture_list *next = capture->next;
 
 		i915_vma_snapshot_put(capture->vma_snapshot);
+		kfree(capture);
 		capture = next;
 	}
 }