mvebu: gen_mvebu_sdcard_img.sh: don't use format directly in printf

Enables proper checking. Matches printf behavior in C.

Found with shellcheck.

Signed-off-by: Rosen Penev <rosenp@gmail.com>
[add prefix to commit title]
Signed-off-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>

target/linux/mvebu/image/gen_mvebu_sdcard_img.sh

@@ -41,7 +41,7 @@ if [ -n "$BOOTLOADER" ]; then
 fi
 
 # generate image file
-printf "Creating $OUTFILE from /dev/zero: "
+printf "Creating %s from /dev/zero: " "$OUTFILE"
 dd if=/dev/zero of="$OUTFILE" bs=512 count=1 >/dev/null
 printf "Done\n"