EliasFano.Build: less iterations in upperBits loop #6829

Job	Run time
test-hive (engine, withdrawals, 0)	6m 45s
test-hive (engine, exchange-capabilities, 0)	3m 48s
test-hive (engine, api, 0)	7m 11s
test-hive (engine, auth, 0)	3m 49s
test-hive (rpc, compat, 23)	3m 3s
test-hive (engine, cancun, 3)	8m 52s
	33m 28s

Provide feedback