arm64: dts: qcom: fix serial output for sm8250-hdk

The uart2 node has been renamed, apply the change to sm8250-hdk dts too so
that serial output works.

Fixes: 91ed0e90

 ("arm64: dts: qcom: add sm8250 hdk dts")
Signed-off-by: Jonathan Marek <jonathan@marek.ca>
Link: https://lore.kernel.org/r/20201123143538.14198-1-jonathan@marek.ca


Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>