JIT: fix fast path for `with-continuation-mark`
JIT: fix fast path for `with-continuation-mark`

Incorrect bitwise shift caused a fast-path test to be too
conservative.

mafagafogigante/racket,mafagafogigante/racket,mafagafogigante/racket,mafagafogigante/racket,mafagafogigante/racket,mafagafogigante/racket,mafagafogigante/racket,mafagafogigante/racket,mafagafogigante/racket