dt-bindings: ufs: qcom: Add SM6350 compatible string

Document the compatible for the UFS found on SM6350.

Signed-off-by: Luca Weiss <luca.weiss@fairphone.com>
Reviewed-by: Krzysztof Kozlowski <krzk@kernel.org>
Reviewed-by: Alim Akhtar <alim.akhtar@samsung.com>
Signed-off-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20220321133318.99406-2-luca.weiss@fairphone.com