syntax: inline getParamLit
syntax: inline getParamLit

The logic is simpler this way. Also makes parameter expansion a tiny bit
faster since the helper function can't be inlined.

name                   old time/op    new time/op    delta
Parse/Vars+Clauses-4     5.10µs ± 0%    5.06µs ± 1%  -0.88%  (p=0.009 n=6+6)

mvdan/sh,mvdan/sh,mvdan/sh,mvdan/sh