of: Preserve "of-display" device name for compatibility

Since commit 241d2fb5 ("of: Make OF framebuffer device names unique"),
as spotted by Frédéric Bonnard, the historical "of-display" device is
gone: the updated logic creates "of-display.0" instead, then as many
"of-display.N" as required.

This means that offb no longer finds the expected device, which prevents
the Debian Installer from setting up its interface, at least on ppc64el.

Fix this by keeping "of-display" for the first device and "of-display.N"
for subsequent devices.

Link: https://bugzilla.kernel.org/show_bug.cgi?id=217328
Link: https://bugs.debian.org/1033058


Fixes: 241d2fb5 ("of: Make OF framebuffer device names unique")
Cc: stable@vger.kernel.org
Cc: Cyril Brulebois <cyril@debamax.com>
Cc: Thomas Zimmermann <tzimmermann@suse.de>
Cc: Helge Deller <deller@gmx.de>
Acked-by: Helge Deller <deller@gmx.de>
Acked-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Michal Suchánek <msuchanek@suse.de>
Link: https://lore.kernel.org/r/20230710174007.2291013-1-robh@kernel.org


Signed-off-by: Rob Herring <robh@kernel.org>