convert-dtsv0-lexer.l: fix memory leak

CID 132822 (#1 of 1): Resource leak (RESOURCE_LEAK)
9. leaked_storage: Variable newname going out of scope leaks the storage it points to

Signed-off-by: Jean-Christophe Dubois <jcd@tribudubois.net>
[dwg: Removed unnecessary hunk]
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>