tuple: make tuple_bless() compilable

tuple_bless() uses a tail call to ffi.gc() with return to the caller.
This tail call uses the current (tuple_bless) frame instead of creating
the frame for the callee (ffi.gc). When JIT tries to compile return from
`ffi.gc()` to the frame below it aborts the trace recording with the
error "NYI: return to lower frame".

This patch replaces the tail call with using additional local variable
returned to the caller right after.

Reviewed-by: Nikita Pettik <korablev@tarantool.org>
Reviewed-by: Igor Munkin <imun@tarantool.org>
Signed-off-by: Igor Munkin <imun@tarantool.org>