configure*: fix typo of HAVE_USERTMPFS

Added on commit 64a8d6a ("compile time option to disable
--private-cache and --tmpfs for regular user").

These are the only occurrences:

    $ git ls-files -z | xargs -0 grep -Fin USERTMPS
    configure:3542:HAVE_USERTMPS=""
    configure.ac:80:HAVE_USERTMPS=""

configure

@@ -3539,7 +3539,7 @@ HAVE_OVERLAYFS=""
 # AC_SUBST(HAVE_OVERLAYFS)
 #])
 
-HAVE_USERTMPS=""
+HAVE_USERTMPFS=""
 # Check whether --enable-usertmpfs was given.
 if test "${enable_usertmpfs+set}" = set; then :
  enableval=$enable_usertmpfs;

configure.ac

@@ -77,7 +77,7 @@ AC_SUBST(HAVE_OVERLAYFS)
 # AC_SUBST(HAVE_OVERLAYFS)
 #])
 
-HAVE_USERTMPS=""
+HAVE_USERTMPFS=""
 AC_ARG_ENABLE([usertmpfs],
  AS_HELP_STRING([--disable-usertmpfs], [disable tmpfs as regular user]))
 AS_IF([test "x$enable_usertmpfs" != "xno"], [