PCI: mvebu: Drop bogus comment above mvebu_pcie_map_registers()

This comment has been there since the driver was introduced, but seems
to be a leftover from previous iterations of the driver. Indeed, we do
not lookup in a list to find the register ranges that matches the
given port/lane, as the "reg" property is in each sub-node
representing a PCI port. There is no lookup involved at all.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>