Add compatible string for pmm8155au pmic found on
the SA8155p-adp board.

Cc: Mark Brown <broonie@kernel.org>
Cc: Bjorn Andersson <bjorn.andersson@linaro.org>
Signed-off-by: NBhupesh Sharma <bhupesh.sharma@linaro.org>
Reviewed-by: NBjorn Andersson <bjorn.andersson@linaro.org>
Link: https://lore.kernel.org/r/20210617051712.345372-3-bhupesh.sharma@linaro.orgSigned-off-by: NMark Brown <broonie@kernel.org>