board/altera/socrates_cyclone5/genimage.cfg: fix offset suffix

For consistency 'offset = 256k' must be 'offset = 256K'

Signed-off-by: Giulio Benetti <giulio.benetti@benettiengineering.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

board/altera/socrates_cyclone5/genimage.cfg

@@ -24,7 +24,7 @@ image uboot.img {
 	partition uboot-full {
 		in-partition-table = "no"
 		image = "u-boot.img"
-		offset = 256k
+		offset = 256K
 	}
 
 	size = 1M