doc/configuration.adoc: fix incorrect number of physical RF channels for B210
doc/configuration.adoc: fix incorrect number of physical RF channels for B210

Change-Id: I58e2bf5dd99e1655ebd2ad80f6ed2bb178f0e88d

osmocom/osmo-trx,osmocom/osmo-trx,osmocom/osmo-trx,osmocom/osmo-trx