arm64: dts: qcom: pmi8950: Correct rev_1250v channel label to mv

This was pointed out in review but never followed up on thanks to
sidetracked discussions about labels vs node names.

Fixes: 0d97fdf3 ("arm64: dts: qcom: Add configuration for PMI8950 peripheral")
Signed-off-by: Marijn Suijten <marijn.suijten@somainline.org>
Reviewed-by: Konrad Dybcio <konrad.dybcio@linaro.org>
Reviewed-by: Luca Weiss <luca@z3ntu.xyz>
Signed-off-by: Bjorn Andersson <andersson@kernel.org>
Link: https://lore.kernel.org/r/20221209215437.1783067-1-marijn.suijten@somainline.org