powerpc/xive: Fix refcount leak in xive_get_max_prio

powerpc/xive: Fix refcount leak in xive_get_max_prio

[ Upstream commit 255b650cbec6849443ce2e0cdd187fd5e61c218c ]

of_find_node_by_path() returns a node pointer with
refcount incremented, we should use of_node_put() on it when done.
Add missing of_node_put() to avoid refcount leak.

Fixes: eac1e731b59e ("powerpc/xive: guest exploitation of the XIVE interrupt controller")
Signed-off-by: Miaoqian Lin <linmq006@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20220605053225.56125-1-linmq006@gmail.com
Signed-off-by: Sasha Levin <sashal@kernel.org>