ARM: dts: at91: sam9x60ek: fix indentation for pinctrl sub-nodes

The indentation went far on the right due to an extra tab for
each pinctrl sub-nodes.

Signed-off-by: Dario Binacchi <dario.binacchi@amarulasolutions.com>
Reviewed-by: Michael Trimarchi <michael@amarulasolutions.com>