drivers: mcb: fix memory leak in chameleon_parse_cells() error path

chameleon_parse_cells() bails out if chameleon descriptor type is
invalid but does not free the storage 'header' points to.

Signed-off-by: Christoph Jaeger <christophjaeger@linux.com>
Signed-off-by: Johannes Thumshirn <johannes.thumshirn@men.de>