mmc: atmel-mci: add missing of_node_put

for_each_child_of_node performs an of_node_get on each iteration, so a
break out the loop requires an of_node_put.

The semantic patch that fixes this problem is as follows
(http://coccinelle.lip6.fr

):

// <smpl>
@@
local idexpression n;
expression e,e1;
iterator name for_each_child_of_node;
@@

 for_each_child_of_node(e1,n) {
   ...
(
   of_node_put(n);
|
   e = n
|
+  of_node_put(n);
?  break;
)
   ...
 }
... when != n
// </smpl>

Signed-off-by: Julia Lawall <Julia.Lawall@lip6.fr>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>