thermal: always use curly brackets when dereferencing array elements

${array[1]} is the recommended way to dereference array elements in
bash.  While $array[1] may work with some implementations of bash, it
is not guaranteed to work.

Signed-off-by: Javi Merino <javi.merino@arm.com>
Acked-by: Sanjay Singh Rawat <sanjay.rawat@linaro.org>
diff --git a/include/thermal_functions.sh b/include/thermal_functions.sh
index eaf378b..bfc6620 100644
--- a/include/thermal_functions.sh
+++ b/include/thermal_functions.sh
@@ -185,7 +185,7 @@
 
     local flag=0
     for cpu in $cpus; do
-	if [ $before_freq_list[$index] -ne $after_freq_list[$index] ] ; then
+	if [ ${before_freq_list[$index]} -ne ${after_freq_list[$index]} ] ; then
 	    flag=1	
 	fi
         index=$((index + 1)) 
@@ -237,7 +237,7 @@
 
     local th_zones=$(ls $THERMAL_PATH | grep "thermal_zone['$MAX_ZONE']")
     for zone in $th_zones; do
-	echo $mode_list[$index] > $THERMAL_PATH/$zone/mode
+	echo ${mode_list[$index]} > $THERMAL_PATH/$zone/mode
         index=$((index + 1))
     done
     return 0