arm64: dts: qcom: ipq6018: Remove unused 'iface_clk' property from dma-controller node

'iface_clk' clock is not used by the
qcom, bam_dma driver, so remove the same from 'ipq6018' dts.

This is a preparatory patch for subsequent patch in
this series which converts the qcom_bam_dma device-tree
binding into YAML format.

Without this change, 'make dtbs_check' leads to the following
error:
 $ arch/arm64/boot/dts/qcom/ipq6018-cp01-c1.dt.yaml:
     dma-controller@7984000: clock-names: ['iface_clk', 'bam_clk']
     is too long

Fix the same.

Cc: Thara Gopinath <thara.gopinath@linaro.org>
Cc: Bjorn Andersson <bjorn.andersson@linaro.org>
Cc: Rob Herring <robh+dt@kernel.org>
Signed-off-by: Bhupesh Sharma <bhupesh.sharma@linaro.org>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Link: https://lore.kernel.org/r/20211013105541.68045-4-bhupesh.sharma@linaro.org