vm_eval.c: use RARRAY_CONST_PTR to aid RGenGC performance

Pointed out by ko1.

* vm_eval.c (vm_call0_body): use RARRAY_CONST_PTR
  (check_funcall_exec): ditto
  [ruby-core:61360]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@45283 b2dd03c8-39d4-4d8f-98ff-823fe69b080e