arm64: dts: qcom: sm8450: align MMC node names with dtschema

The bindings expect "mmc" for MMC/SDHCI nodes:

  qcom/sm8450-sony-xperia-nagara-pdx223.dtb: sdhci@8804000: $nodename:0: 'sdhci@8804000' does not match '^mmc(@.*)?$'

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>