nfs4: Fix kmemleak when allocate slot failed
This is an automated ID intended to aid in discovery of potential security vulnerabilities. The actual impact and attack plausibility have not yet been proven. This ID is fixed in Linux Kernel version v5.15.78 by commit 24641993a7dce6b1628645f4e1d97ca06c9f765d, it was introduced in version v3.12 by commit abf79bb341bf52f75f295b850abdf5f78f584311. For more details please see the references link.