openrisc: Fix a memory leak

[ Upstream commit c019d92457826bb7b2091c86f36adb5de08405f9 ]

'setup_find_cpu_node()' take a reference on the node it returns.
This reference must be decremented when not needed anymore, or there will
be a leak.

Add the missing 'of_node_put(cpu)'.

Note that 'setup_cpuinfo()' that also calls this function already has a
correct 'of_node_put(cpu)' at its end.

Fixes: 9d02a428 ("OpenRISC: Boot code")
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Signed-off-by: Stafford Horne <shorne@gmail.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>