leds: netxbig: Add of_node_put() in netxbig_leds_get_of_pdata()

The variable gpio_ext_np in the function netxbig_leds_get_of_pdata takes
the value returned by of_parse_phandle; hence, it must be put in order
to prevent a memory leak. Add an of_node_put for gpio_ext_np before a
return statement, and move a pre-existing of_node_put statement to right
after the last usage of this variable.
Issue found with Coccinelle.

Signed-off-by: Nishka Dasgupta <nishkadg.linux@gmail.com>
Acked-by: Pavel Machek <pavel@ucw.cz>
Signed-off-by: Jacek Anaszewski <jacek.anaszewski@gmail.com>