sysmobts: Change the ARRAY_SIZE to a constant number
sysmobts: Change the ARRAY_SIZE to a constant number

The parameter "uint8_t mute_state[8]" is actually a "uint8_t *mute_state"
so the ARRAY_SIZE is not what we think it is.

Fixes: Coverity CID 1125885

osmocom/osmo-bts,geosphere/osmo-bts,geosphere/osmo-bts,telenoobie/osmo-bts,geosphere/osmo-bts,telenoobie/osmo-bts,osmocom/osmo-bts,telenoobie/osmo-bts,telenoobie/osmo-bts,osmocom/osmo-bts,geosphere/osmo-bts