NFS: Prevent resource leak in nfs_alloc_server()

NFS: Prevent resource leak in nfs_alloc_server()

It was overlooked to call ida_free() after a failed nfs_alloc_iostats() call.
Thus add the missed function call in an if branch.

Fixes: 1c7251187dc067a6d460cf33ca67da9c1dd87807 ("NFS: add superblock sysfs entries")
Cc: stable@vger.kernel.org
Reported-by: Christophe Jaillet <christophe.jaillet@wanadoo.fr>
Closes: https://lore.kernel.org/linux-nfs/1c8e10c9-def7-4f0d-8aa1-23c8035a38c8@wanadoo.fr/
Signed-off-by: Markus Elfring <elfring@users.sourceforge.net>
Signed-off-by: Anna Schumaker <anna.schumaker@hammerspace.com>