drm: re-enable error handling

drm_legacy_ctxbitmap_next() returns idr_alloc() which can return
-ENOMEM, -EINVAL or -ENOSPC none of which are -1 . but the call sites
of drm_legacy_ctxbitmap_next() seem to be assuming that the error case
would be -1 (original return of drm_ctxbitmap_next() prior to 2.6.23
was actually -1). Thus reenable error handling by checking for < 0.
Signed-off-by: Nicholas Mc Guire <hofrat@osadl.org>
Fixes: 62968144 ("drm: convert drm context code to use Linux idr")
Signed-off-by: Sean Paul <seanpaul@chromium.org>
Link: https://patchwork.freedesktop.org/patch/msgid/1531571532-22733-1-git-send-email-hofrat@osadl.org

drivers/gpu/drm/drm_context.c

@@ -372,7 +372,7 @@ int drm_legacy_addctx(struct drm_device *dev, void *data,
 		ctx->handle = drm_legacy_ctxbitmap_next(dev);
 	}
 	DRM_DEBUG("%d\n", ctx->handle);
-	if (ctx->handle == -1) {
+	if (ctx->handle < 0) {
 		DRM_DEBUG("Not enough free contexts.\n");
 		/* Should this return -EBUSY instead? */
 		return -ENOMEM;