arm64: dts: qcom: sm6115: Cleanup USB node's label

There is only one USB controller present on SM6115 / SM4250
Qualcomm SoC, so drop the numbering used with USB node's label
names in the dtsi and the related sm4250-oneplus-billie2.dts.

Reviewed-by: Konrad Dybcio <konrad.dybcio@linaro.org>
Signed-off-by: Bhupesh Sharma <bhupesh.sharma@linaro.org>
Signed-off-by: Bjorn Andersson <andersson@kernel.org>
Link: https://lore.kernel.org/r/20230314083633.1882214-2-bhupesh.sharma@linaro.org