scripts/gen_image_generic.sh: fix more shellcheck warnings
Fixes following shellcheck warnings:
In scripts/gen_image_generic.sh line 20:
cyl=$(( (KERNELSIZE + ROOTFSSIZE) * 1024 * 1024 / (head * sect * 512)))
^-^ SC2034: cyl appears unused. Verify use (or export if used externally).
--
In scripts/gen_image_generic.sh line 34:
[ -n "$PADDING" ] && dd if=/dev/zero of="$OUTPUT" bs=512 seek="$(($ROOTFSOFFSET + $ROOTFSSIZE))" conv=notrunc count="$sect"
^-----------^ SC2004: $/${} is unnecessary on arithmetic variables.
--
In scripts/gen_image_generic.sh line 35:
mkfs.fat -n kernel -C "$OUTPUT.kernel" -S 512 "$(($KERNELSIZE / 1024))"
^---------^ SC2004: $/${} is unnecessary on arithmetic variables.
Signed-off-by: Petr Štetiar <ynezz@true.cz>