[writeboost] add destroy_work_on_stack in dm_safe_io_internal

destroy_work_on_stack must be pair of INIT_WORK_ONSTACK

Signed-off-by: Akira Hayakawa <ruby.wktk@gmail.com>
Merge pull request #6 from akiradeveloper/feature/fix-work-on-stack

[writeboost] add destroy_work_on_stack in dm_safe_io_internal