net: gianfar: Add of_node_put() before goto statement

Every iteration of for_each_available_child_of_node() decrements
reference count of the previous node, however when control
is transferred from the middle of the loop, as in the case of
a return or break or goto, there is no decrement thus ultimately
resulting in a memory leak.

Fix a potential memory leak in gianfar.c by inserting of_node_put()
before the goto statement.

Issue found with Coccinelle.

Signed-off-by: Sumera Priyadarsini <sylphrenadin@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>