osd/OSD.h: fix try_stop_deletion

Fix try_stop_deletion(): The comment above the while loop says "If we are
in DELETING_DIR or DELETED_DIR", but the while loop checks for DELETING_DIR
twice. Change one check to DELETED_DIR otherwise on state get missed.

Signed-off-by: Danny Al-Gaaf <danny.al-gaaf@bisect.de>
Merge pull request #274 from dalgaaf/wip-da-fix-osd_h

osd/OSD.h: fix try_stop_deletion

Reviewed-by: Sam Just <sam.just@inktank.com>