powerpc/mpc5xxx: Add missing fwnode_handle_put()

In mpc5xxx_fwnode_get_bus_frequency(), we should add
fwnode_handle_put() when break out of the iteration
fwnode_for_each_parent_node() as it will automatically
increase and decrease the refcounter.

Fixes: de06fba6 ("powerpc/mpc5xxx: Switch mpc5xxx_get_bus_frequency() to use fwnode")
Signed-off-by: Liang He <windhl@126.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20230322030423.1855440-1-windhl@126.com