ARM: dts: qcom: mdm9615: fix memory node for Sierra Wireless WP8548

Specify unit address for the memory node, to match the reg.

Signed-off-by: David Heidelberg <david@ixit.cz>
[bjorn: Rewrote commit message]
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Link: https://lore.kernel.org/r/20211020234431.298310-1-david@ixit.cz