ARM: at91: at91sam9x5: fix usart3 pinctrl name

The renaming of pinctrl_uart3 to pinctrl_usart3 was missed in
commit 9e3129e9 (ARM: at91: fix usart/uart namimg in pinctrl).
Signed-off-by: Robert Nelson <robertcnelson@gmail.com>
Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>

arch/arm/boot/dts/at91sam9x5.dtsi

@@ -197,7 +197,7 @@ pinctrl_usart2_sck: usart2_sck-0 {
 				};
 
 				usart3 {
-					pinctrl_uart3: usart3-0 {
+					pinctrl_usart3: usart3-0 {
 						atmel,pins =
 							<2 23 0x2 0x1	/* PC22 periph B with pullup */
 							 2 23 0x2 0x0>;	/* PC23 periph B */