Unfortunately there are three problems: the "^t" escape for a tab character in a sed(1) regex is not sufficiently portable, the backslashes in the sed(1) command would have to be escaped against the surrounding double-quotes and the capturing regex also would capture trailing whitespaces. I see no portable and at the same time generic enough way to solve this with sed(1). Instead awk(1) works far more reasonable here.

ntp/rc.ntp

@@ -13,7 +13,7 @@
     ntp_log_complevel="9"
 
 %common
-    ntp_pidfile=`grep "^pidfile" @l_prefix@/etc/ntp/ntp.conf | sed -e "s;[^ ^t]*[ ^t]*\(.*\)$;\1;"`
+    ntp_pidfile=`grep "^pidfile" @l_prefix@/etc/ntp/ntp.conf | awk '{ printf("%s", $2); }'`
     ntp_signal () {
         [ -f $ntp_pidfile ] && kill -$1 `cat $ntp_pidfile`
     }