extract_utils: template: use quotation marks and variable curly braces consistently

* This makes sure that multi-word arguments are passed correctly from
  extract-files.sh towards the common extract_utils helper. An example
  would be extract-files --section "Hello World".
* IMPORTANT: device repositories that use a device/common split
  typically do something like this to invoke the common script from the
  device one:

  ${MY_DIR}/../common/extract-files.sh $@

  This is incorrect because the quotation marks are missing, and will
  lead to incorrect parameter parsing. The correct way is:

  ${MY_DIR}/../common/extract-files.sh "$@"

* The curly braces are only for cosmetic consistency.

Change-Id: Idf0885546379f47e675ec5e9dfb304706e512129
Signed-off-by: Vladimir Oltean <olteanv@gmail.com>
diff --git a/build/templates/extract-files.sh b/build/templates/extract-files.sh
index fd6e7eb..c6f3926 100755
--- a/build/templates/extract-files.sh
+++ b/build/templates/extract-files.sh
@@ -23,41 +23,41 @@
 
 # Load extract_utils and do some sanity checks
 MY_DIR="${BASH_SOURCE%/*}"
-if [[ ! -d "$MY_DIR" ]]; then MY_DIR="$PWD"; fi
+if [[ ! -d "${MY_DIR}" ]]; then MY_DIR="${PWD}"; fi
 
-LINEAGE_ROOT="$MY_DIR"/../../..
+LINEAGE_ROOT="${MY_DIR}/../../.."
 
-HELPER="$LINEAGE_ROOT"/vendor/lineage/build/tools/extract_utils.sh
-if [ ! -f "$HELPER" ]; then
-    echo "Unable to find helper script at $HELPER"
+HELPER="${LINEAGE_ROOT}/vendor/lineage/build/tools/extract_utils.sh"
+if [ ! -f "${HELPER}" ]; then
+    echo "Unable to find helper script at ${HELPER}"
     exit 1
 fi
-. "$HELPER"
+source "${HELPER}"
 
 # Default to sanitizing the vendor folder before extraction
 CLEAN_VENDOR=true
 
 while [ "$1" != "" ]; do
-    case $1 in
+    case "$1" in
         -n | --no-cleanup )     CLEAN_VENDOR=false
                                 ;;
         -s | --section )        shift
-                                SECTION=$1
+                                SECTION="$1"
                                 CLEAN_VENDOR=false
                                 ;;
-        * )                     SRC=$1
+        * )                     SRC="$1"
                                 ;;
     esac
     shift
 done
 
-if [ -z "$SRC" ]; then
+if [ -z "${SRC}" ]; then
     SRC=adb
 fi
 
 # Initialize the helper
-setup_vendor "$DEVICE" "$VENDOR" "$LINEAGE_ROOT" false "$CLEAN_VENDOR"
+setup_vendor "${DEVICE}" "${VENDOR}" "${LINEAGE_ROOT}" false "${CLEAN_VENDOR}"
 
-extract "$MY_DIR"/proprietary-files.txt "$SRC" "$SECTION"
+extract "${MY_DIR}/proprietary-files.txt" "${SRC}" "${SECTION}"
 
-"$MY_DIR"/setup-makefiles.sh
+"${MY_DIR}/setup-makefiles.sh"