Fix missing vdev names in zpool status output

Fix missing vdev names in zpool status output

Commit 858219c makes more sense down below in the 'if (verbose)'
section of the code.  Initially, buf and path will never point
to the same location.  Once 'path = buf' is set on a raidz vdev,
the code may drop into the verbose section depending on the
verbose flag.  In here, using a tmpbuf makes sense since now
'buf == path'.

This issue does not occur in the upstream Solaris code because
their implementations of snprintf() allow for buf and path to
be the same address.

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #57