arm64: dts: qcom: qcs6390-rb3gen2: use modem.mbn for modem DSP

arm64: dts: qcom: qcs6390-rb3gen2: use modem.mbn for modem DSP

Newer boards should always use squashed MBN firmware instead of split
MDT+bNN. Use qcom/qcs6490/modem.mbn as the firmware for the modem on
RB3gen2.

Fixes: ac6d35b9b74c ("arm64: dts: qcom: qcs6490-rb3gen2: Enable various remoteprocs")
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Reviewed-by: Konrad Dybcio <konradybcio@kernel.org>
Link: https://lore.kernel.org/r/20240907-rb3g2-fixes-v1-1-eb9da98e9f80@linaro.org
Signed-off-by: Bjorn Andersson <andersson@kernel.org>