ARM: at91: at91sam9g45: set default mmc pinctrl-names

pinctrl-names property was missing from mmc nodes.

Cc: <stable@vger.kernel.org> #3.11+
Signed-off-by: Ludovic Desroches <ludovic.desroches@atmel.com>
Acked-by: Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>
Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>