MFC: r228211

MFC: r228211

It doesn't make much sense to check whether child is NULL after already
having dereferenced it. We either should generally check the device_t's
supplied to bus functions before using them (which we seem to virtually
never do) or just assume that they are not NULL.
While at it make this code fit 78 columns.

Found with:	Coverity Prevent(tm)
CID:		4230

git-svn-id: svn://svn.freebsd.org/base/stable/9@230740 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f