board/asus/tinker-s/post-build.sh: add quoting to make shellcheck happy

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

board/asus/tinker-s/post-build.sh

@@ -1,9 +1,9 @@
 #!/bin/sh
 
 MKIMAGE=$HOST_DIR/bin/mkimage
-BOARD_DIR="$(dirname $0)"
+BOARD_DIR="$(dirname "$0")"
 
-$MKIMAGE -n rk3288 -T rksd -d $BINARIES_DIR/u-boot-tpl.bin $BINARIES_DIR/u-boot-tpl.img
-cat $BINARIES_DIR/u-boot-tpl.img $BINARIES_DIR/u-boot-spl-dtb.bin > $BINARIES_DIR/u-boot-tpl-spl-dtb.img
+$MKIMAGE -n rk3288 -T rksd -d "$BINARIES_DIR"/u-boot-tpl.bin "$BINARIES_DIR"/u-boot-tpl.img
+cat "$BINARIES_DIR"/u-boot-tpl.img "$BINARIES_DIR"/u-boot-spl-dtb.bin > "$BINARIES_DIR"/u-boot-tpl-spl-dtb.img
 
-install -m 0644 -D $BOARD_DIR/extlinux.conf $TARGET_DIR/boot/extlinux/extlinux.conf
+install -m 0644 -D "$BOARD_DIR"/extlinux.conf "$TARGET_DIR"/boot/extlinux/extlinux.conf