dt-bindings: Fix missing '/schemas' in $ref paths

Absolute paths in $ref should always begin with '/schemas'. The tools
mostly work with it omitted, but for correctness the path should be
everything except the hostname as that is taken from the schema's $id
value. This scheme is defined in the json-schema spec.

Cc: Hector Martin <marcan@marcan.st>
Cc: Sven Peter <sven@svenpeter.dev>
Cc: Andrew Lunn <andrew@lunn.ch>
Cc: Vivien Didelot <vivien.didelot@gmail.com>
Cc: Florian Fainelli <f.fainelli@gmail.com>
Cc: Vladimir Oltean <olteanv@gmail.com>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Jakub Kicinski <kuba@kernel.org>
Cc: Paolo Abeni <pabeni@redhat.com>
Cc: Mark Brown <broonie@kernel.org>
Cc: Chunfeng Yun <chunfeng.yun@mediatek.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Mukesh Savaliya <msavaliy@codeaurora.org>
Cc: Akash Asthana <akashast@codeaurora.org>
Cc: Bayi Cheng <bayi.cheng@mediatek.com>
Cc: Chuanhong Guo <gch981213@gmail.com>
Cc: Min Guo <min.guo@mediatek.com>
Cc: netdev@vger.kernel.org
Cc: linux-spi@vger.kernel.org
Cc: linux-usb@vger.kernel.org
Signed-off-by: Rob Herring <robh@kernel.org>
Acked-by: Jakub Kicinski <kuba@kernel.org>
Acked-by: Mark Brown <broonie@debian.org>
Link: https://lore.kernel.org/r/20220325215652.525383-1-robh@kernel.org