uboot-sign: Fix index error in concat_dtb_helper() with multiple configs

Commit 60774248a5 solves issues when i or j
have been set in other shell functions.

Since j is not unset after the inner loop, the image will only be copied
for the first configuration.

Unsetting i and j after the loops also prevents index issues in other functions.

(From OE-Core rev: f6de96c9fa8d0b6c81c32016f342ad93c8940d9e)

Signed-off-by: Florian Amstutz <florian.amstutz@scs.ch>
Signed-off-by: Steve Sakoman <steve@sakoman.com>

meta/classes/uboot-sign.bbclass

@@ -137,8 +137,7 @@ concat_dtb_helper() {
 
 			if [ -n "${UBOOT_CONFIG}" ]
 			then
-				i=0
-				j=0
+				unset i j
 				for config in ${UBOOT_MACHINE}; do
 					i=$(expr $i + 1);
 					for type in ${UBOOT_CONFIG}; do
@@ -146,9 +145,12 @@ concat_dtb_helper() {
 						if [ $j -eq $i ]
 						then
 							cp ${UBOOT_IMAGE} ${B}/${CONFIG_B_PATH}/u-boot-$type.${UBOOT_SUFFIX}
+							break
 						fi
 					done
+					unset j
 				done
+				unset i
 			fi
 		else
 			bbwarn "Failure while adding public key to u-boot binary. Verified boot won't be available."