meta-quanta: fix shellcheck issues

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: I189baf142cc86d44ebbf615edd3bb0ec1785be8d
diff --git a/meta-quanta/meta-gbs/recipes-gbs/gbs-bios-update/files/bios-verify.sh b/meta-quanta/meta-gbs/recipes-gbs/gbs-bios-update/files/bios-verify.sh
index 3da25e4..ac4ee1d 100644
--- a/meta-quanta/meta-gbs/recipes-gbs/gbs-bios-update/files/bios-verify.sh
+++ b/meta-quanta/meta-gbs/recipes-gbs/gbs-bios-update/files/bios-verify.sh
@@ -14,11 +14,11 @@
 
 if [ -e $IMAGE_FILE ] && [ -e $SIG_FILE ];
 then
-    sha256_image=`sha256sum "$IMAGE_FILE" | awk '{print $1}'`
-    sha256_file=`awk '{print $1}' $SIG_FILE`
+    sha256_image=$(sha256sum "$IMAGE_FILE" | awk '{print $1}')
+    sha256_file=$(awk '{print $1}' $SIG_FILE)
 fi
 
-if [[ $sha256_image != $sha256_file ]];
+if [ "$sha256_image" != "$sha256_file" ];
 then
     echo "bios image verify fail."
     rm -f $IMAGE_FILE