livetree: simplify condition in get_node_by_path

The "strlen && strprefixeq" check in get_node_by_path is
excessive, since strlen is checked in strprefixeq macro
internally. Thus, "strlen(child->name) == p-path"
conjunct duplicates after macro expansion and could
be removed.

Signed-off-by: Denis Efremov <efremov@linux.com>
Message-Id: <20190827204148.20604-1-efremov@linux.com>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>