Consolidate finding of a root bridge and getting its handle to the one
inline function. It's cut & pasted on multiple places. Use this new
inline in those.

Cc: kristen.c.accardi@intel.com
Acked-by: NAlex Chiang <achiang@hp.com>
Signed-off-by: NJiri Slaby <jirislaby@gmail.com>
Signed-off-by: NJesse Barnes <jbarnes@virtuousgeek.org>