Don't leak string in parse_define(..) when a macro has been found
and the parser token != TOK_ASSIGN

MFC after: 1 week
CID: 1007187, 1007188
Reported by: Coverity
Obtained from: Isilon OneFS (part of r445479)
Submitted by: Miles Ohlrich <miles.ohlrich@isilon.com>
Sponsored by: EMC / Isilon Storage Division