ARM: dts: qcom: sdx55: fix IPA interconnect definitions

The first two interconnects defined for IPA on the SDX55 SoC are
really two parts of what should be represented as a single path
between IPA and system memory.

Fix this by combining the "memory-a" and "memory-b" interconnects
into a single "memory" interconnect.

Reported-by: David Heidelberg <david@ixit.cz>
Tested-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Signed-off-by: Alex Elder <elder@linaro.org>
Signed-off-by: David S. Miller <davem@davemloft.net>