nvme: fix potential memory leak in option parsing

nvme: fix potential memory leak in option parsing

[ Upstream commit 59a2f3f00fd744dbad22593f47552037d3154ca6 ]

When specifying same string type option several times,
current option parsing may cause memory leak. Hence,
call kfree for previous one in this case.

Signed-off-by: Chengguang Xu <cgxu519@gmx.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Signed-off-by: Keith Busch <keith.busch@intel.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>