Fix error in imm()
Fix error in imm()

imm() was reserving space for only a pointer to Symbol,
not for the symbol itself.

8l/scc,k0gaMSX/scc,k0gaMSX/kcc,8l/scc,k0gaMSX/scc,k0gaMSX/scc,k0gaMSX/kcc,8l/scc