fs/exofs: fix potential memory leak in mount option parsing

[ Upstream commit 515f1867addaba49c1c6ac73abfaffbc192c1db4 ]

There are some cases can cause memory leak when parsing
option 'osdname'.

Signed-off-by: Chengguang Xu <cgxu519@gmx.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Sasha Levin <sashal@kernel.org>