mfd: syscon: Call of_node_put() only when of_parse_phandle() takes a ref

mfd: syscon: Call of_node_put() only when of_parse_phandle() takes a ref

of_parse_phandle() returns a device_node with refcount incremented, which
the callee needs to call of_node_put() on when done. We should only call
of_node_put() when the property argument is provided though as otherwise
nothing has taken a reference on the node.

Fixes: 45330bb43421 ("mfd: syscon: Allow property as NULL in syscon_regmap_lookup_by_phandle")
Signed-off-by: Peter Griffin <peter.griffin@linaro.org>
Link: https://lore.kernel.org/r/20240220115012.471689-2-peter.griffin@linaro.org
Signed-off-by: Lee Jones <lee@kernel.org>