ARM: dts: aspeed: rainier: Add line-name checkstop

Rainier uses GPIO B6 as the checkstop GPIO. Define the line-name
so that this GPIO can be found by name.

Signed-off-by: Ben Tyner <ben.tyner@ibm.com>
Signed-off-by: Joel Stanley <joel@jms.id.au>

arch/arm/boot/dts/aspeed-bmc-ibm-rainier.dts

@@ -73,7 +73,7 @@
 &gpio0 {
 	gpio-line-names =
 	/*A0-A7*/	"","","","","","","","",
-	/*B0-B7*/	"","","","","","","","",
+	/*B0-B7*/	"","","","","","","checkstop","",
 	/*C0-C7*/	"","","","","","","","",
 	/*D0-D7*/	"","","","","","","","",
 	/*E0-E7*/	"","","","","","","","",