powerpc/52xx: Add missing of_node_put() in media5200.c

In media5200_init_irq(), of_find_compatible_node() will return a
node pointer with refcount incremented. The reference should be dropped
with of_node_put() in the failure path or when it is not used anymore.

Don't worry about 'fpga_np == NULL' as of_node_put() can correctly
handle that.

Signed-off-by: Liang He <windhl@126.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20220616144007.3987743-1-windhl@126.com