ARM: exynos: Fix refcount leak in exynos_map_pmu

ARM: exynos: Fix refcount leak in exynos_map_pmu

of_find_matching_node() returns a node pointer with refcount
incremented, we should use of_node_put() on it when not need anymore.
Add missing of_node_put() to avoid refcount leak.
of_node_put() checks null pointer.

Fixes: d8e7cea6892e ("ARM: EXYNOS: Add support for mapping PMU base address via DT")
Signed-off-by: Miaoqian Lin <linmq006@gmail.com>
Link: https://lore.kernel.org/r/20220523145513.12341-1-linmq006@gmail.com
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>