query: Improve efficiency of 'USE' statement detection
query: Improve efficiency of 'USE' statement detection

Benchmark results for a 80 character statement that does not start with
'use':

Before: 1927 ns/op   192 B/op   2 allocs/op
After:  142 ns/op      6 B/op   2 allocs/op

brandscreen/gocql,lytics/gocql,nikandfor/gocql,kelwang/gocql,kelwang/gocql,matope/gocql,tempbottle/gocql,revinate/gocql,gocql/gocql,hackintoshrao/gocql,brandscreen/gocql,i/gocql,tempbottle/gocql,gus/gocql,Zariel/gocql,aai/gocql,tempbottle/gocql,kelwang/gocql,hackintoshrao/gocql,gocql/gocql,matope/gocql,adamweiner/gocql,nikandfor/gocql,CrowdSurge/gocql,nikandfor/gocql,lytics/gocql,CrowdSurge/gocql,hackintoshrao/gocql,brandscreen/gocql,znly/gocql,revinate/gocql,gus/gocql,mailgun/gocql,vrischmann/gocql,vrischmann/gocql,adamweiner/gocql,adamweiner/gocql,ChannelMeter/gocql,aai/gocql,lytics/gocql,mailgun/gocql,ChannelMeter/gocql,znly/gocql,i/gocql,Zariel/gocql,matope/gocql