tmpfiles.sh: small fixes

Change "sort | uniq" to "sort -u". Also, change `...` to $(...).

X-Gentoo-Bug: 493736
X-Gentoo-Bug-URL: https://bugs.gentoo.org/show_bug.cgi?id=493736

sh/tmpfiles.sh.in

@@ -234,7 +234,7 @@ for d in ${tmpfiles_dirs} ; do
 		[ -f $f ] && tmpfiles_basenames="${tmpfiles_basenames}\n${f##*/}"
 	done # for f in ${d}
 done # for d in ${tmpfiles_dirs}
-tmpfiles_basenames="`printf "${tmpfiles_basenames}\n" | sort | uniq`"
+tmpfiles_basenames="$(printf "${tmpfiles_basenames}\n" | sort -u )"
 
 for b in $tmpfiles_basenames ; do
 	real_f=''