migration/vmstate: Remove redundant statement in vmstate_save_state_v()

The "ret" has been assigned in all branches. It didn't need to be
 assigned separately.

Clang static code analyzer show warning:
  migration/vmstate.c:365:17: warning: Value stored to 'ret' is never read
                ret = 0;
                ^     ~

Reported-by: Euler Robot <euler.robot@huawei.com>
Signed-off-by: Chen Qun <kuhn.chenqun@huawei.com>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Signed-off-by: Juan Quintela <quintela@redhat.com>

migration/vmstate.c

@@ -362,7 +362,6 @@ int vmstate_save_state_v(QEMUFile *f, const VMStateDescription *vmsd,
             }
             for (i = 0; i < n_elems; i++) {
                 void *curr_elem = first_elem + size * i;
-                ret = 0;
 
                 vmsd_desc_field_start(vmsd, vmdesc_loop, field, i, n_elems);
                 old_offset = qemu_ftell_fast(f);