Revert "drm/bridge: Introduce drm_bridge_get_next_bridge()"

This reverts commit 9b2f5844.

It breaks the Android kernel api and was added only because of a tiny
drm driver bugfix for an issue that can not ever really be hit, so it is
safe to revert.

Bug: 161946584
Change-Id: If2efa0957f552df8b36a9a30cd2f03b0d59f5e88
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>