rnbd-clt: fix refcount underflow in device unmap path#478

blktests-ci[bot] wants to merge 2 commits intolinus-master_baselinux-blktests/linux-block:linus-master_basefrom

series/1041453=>linus-masterlinux-blktests/linux-block:series/1041453=>linus-masterCopy head branch name to clipboard