board/kontron/smarc-sal28/genimage.cfg: fix option suffix

Option 'offset = 4k' must be 'offset = 4K'.

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

board/kontron/smarc-sal28/genimage.cfg

@@ -4,7 +4,7 @@ image sdcard-emmc.img {
 	}
 
 	partition rcw {
-		offset = 4k
+		offset = 4K
 		in-partition-table = "no"
 		image = "rcw.bin"
 	}