setup-disk: fix detection of volume group

when we have a device like /dev/mapper/vg0-lv_root, then will the LV
name not match with lvs' first column.

setup-disk.in

@@ -152,7 +152,7 @@ supported_boot_fs() {
 
 find_volume_group() {
 	local lv=${1##*/}
-	lvs --noheadings "$1" | awk "\$1 == \"$lv\" {print \$2}"
+	lvs --noheadings "$1" | awk '{print $2}'
 }
 
 find_pvs_in_vg() {