spi: dt-bindings: drop unneeded quotes

Cleanup by removing unneeded quotes from refs and redundant blank lines.
No functional impact except adjusting to preferred coding style.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: Andrew Jeffery <andrew@aj.id.au> # aspeed
Reviewed-by: Neil Armstrong <neil.armstrong@linaro.org> # meson
Reviewed-by: Patrice Chotard <patrice.chotard@foss.st.com> # st
Reviewed-by: Heiko Stuebner <heiko@sntech.de> # rockchip
Reviewed-by: Serge Semin <fancer.lancer@gmail.com> # synopsys
Acked-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20230124083342.34869-1-krzysztof.kozlowski@linaro.org


Signed-off-by: Mark Brown <broonie@kernel.org>