bus_attach_children.9: fix typo
s/DEVICE_ATTACH/DEVICE_DETACH
Approved by: re (cperciva)
Reviewed by: ziaee
MFC after: 3 days
Differential Revision: https://reviews.freebsd.org/D53449
(cherry picked from commit 9b9c726df1e214afa122873395a3ac32dd80ae6b)
(cherry picked from commit c14f97c16b59422ddfd43d9a677f9360004bc23b)