TT#15855 Fix shellcheck warnings for debian/ngcp-rtpengine-kernel-dkms.prerm

Change-Id: I7d103ab75e64c2e5bcda4f7c2096701104ae1fad

debian/ngcp-rtpengine-kernel-dkms.prerm

@@ -5,8 +5,8 @@ set -e
 package=ngcp-rtpengine-kernel-dkms
 name=ngcp-rtpengine
 
-version=`dpkg-query -W -f='${Version}' "$package" \
-        |rev|cut -d- -f2-|rev|cut -d':' -f2|tr -d "\n"`
+version=$(dpkg-query -W -f="\${Version}" "$package" \
+        |rev|cut -d- -f2-|rev|cut -d':' -f2|tr -d "\n")
 
 if [ -x /usr/sbin/ngcp-virt-identify ]; then
 	if /usr/sbin/ngcp-virt-identify --type container; then