drm/i915/gem: Fix error path to unlock if the GEM context is closed

When inside the lock, remember to unlock even if you want to leave
early.
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Fixes: a4e7ccda ("drm/i915: Move context management under GEM")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191106144155.25727-1-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/gem/i915_gem_context.c

@@ -1136,7 +1136,7 @@ static int set_ppgtt(struct drm_i915_file_private *file_priv,
 
 	if (i915_gem_context_is_closed(ctx)) {
 		err = -ENOENT;
-		goto out;
+		goto unlock;
 	}
 
 	if (vm == rcu_access_pointer(ctx->vm))