build: make device tree arg really optional in mkits.sh

If no device tree is given there is no node generated, but
the configuration does still include the name of the missing node.
This will result in a successful build fit image, but bootm does
throw a error message if we want to boot the bad configuration.

Signed-off-by: Johann Neuhauser <jneuhauser@dh-electronics.com>
(cherry picked from commit 205e0939f0)

scripts/mkits.sh

@@ -59,7 +59,7 @@ ARCH_UPPER=`echo $ARCH | tr '[:lower:]' '[:upper:]'`
 
 # Conditionally create fdt information
 if [ -n "${DTB}" ]; then
-	FDT="
+	FDT_NODE="
 		fdt@1 {
 			description = \"${ARCH_UPPER} OpenWrt ${DEVICE} device tree blob\";
 			data = /incbin/(\"${DTB}\");
@@ -74,6 +74,7 @@ if [ -n "${DTB}" ]; then
 			};
 		};
 "
+	FDT_PROP="fdt = \"fdt@1\";"
 fi
 
 # Create a default, fully populated DTS file
@@ -100,9 +101,7 @@ DATA="/dts-v1/;
 				algo = \"sha1\";
 			};
 		};
-
-${FDT}
-
+${FDT_NODE}
 	};
 
 	configurations {
@@ -110,7 +109,7 @@ ${FDT}
 		${CONFIG} {
 			description = \"OpenWrt\";
 			kernel = \"kernel@1\";
-			fdt = \"fdt@1\";
+			${FDT_PROP}
 		};
 	};
 };"