binutils/bfd: fix printf-like format strings for "bfd *" arguments

There is a special format argument '%B' that directly handles values
of type 'bfd *', they must be used instead of '%s'.  Manifestations
of this bug can be seen in ld(1) error messages, for example,
  http://lists.freebsd.org/pipermail/freebsd-current/2013-August/043580.html
  http://lists.freebsd.org/pipermail/freebsd-current/2013-October/045404.html