xfs: use kvfree() in xfs_ioc_attr_list()

Wrongly converted from kmem_free() to kfree().

Reported-by: Matthew Wilcox <willy@infradead.org>
Fixes: 49292576

 ("xfs: convert kmem_free() for kvmalloc users to kvfree()")
Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Chandan Babu R <chandanbabu@kernel.org>