mvebu: cortexa72: fix ImageBuilder for IEI Puzzle devices

The line trying to generate the standard sdcard.img.gz fails due to
boot.scr not being generated.
Remove the line in order to use the default sdcard.img.gz which is
exactly the same but includes generating the boot.scr file.

Signed-off-by: Daniel Golle <[email protected]>

target/linux/mvebu/image/cortexa72.mk

@@ -68,7 +68,6 @@ define Device/iei_puzzle-m901
   DEVICE_VENDOR := iEi
   DEVICE_MODEL := Puzzle-M901
   SOC := cn9131
-  IMAGE/sdcard.img.gz := boot-img-ext4 | sdcard-img-ext4 | gzip | append-metadata
 endef
 TARGET_DEVICES += iei_puzzle-m901
 
@@ -77,6 +76,5 @@ define Device/iei_puzzle-m902
   DEVICE_VENDOR := iEi
   DEVICE_MODEL := Puzzle-M902
   SOC := cn9132
-  IMAGE/sdcard.img.gz := boot-img-ext4 | sdcard-img-ext4 | gzip | append-metadata
 endef
 TARGET_DEVICES += iei_puzzle-m902