Fix the error checking, broken on r273337, to _not_ ignore controller
errors.

Without this fix you can't even scan the bus (all operations will always
succeed).

MFC with:	r273337
Pointy hat to:	loos


git-svn-id: svn+ssh://svn.freebsd.org/base/head@274415 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f