vfs_domount_update(): ensure that 'goto end' works
We need to vfs_op_enter()/vn_seqc_write_start() before jumping to
cleanup.
PR: 274992
Reported by: trasz
Sponsored by: The FreeBSD Foundation
MFC after: 3 days
Fixes: 9ef7a491a4236810e50f0a2ee8d52f5c4bb02c64