tree-wide: fix write_string_file() user that should not create files

The latest consolidation cleanup of write_string_file() revealed some users
of that helper which should have used write_string_file_no_create() in the
past but didn't. Basically, all existing users that write to files in /sys
and /proc should not expect to write to a file which is not yet existant.

src/basic/smack-util.c

@@ -139,7 +139,7 @@ int mac_smack_apply_pid(pid_t pid, const char *label) {
                 return 0;
 
         p = procfs_file_alloca(pid, "attr/current");
-        r = write_string_file(p, label, WRITE_STRING_FILE_CREATE);
+        r = write_string_file(p, label, 0);
         if (r < 0)
                 return r;
 #endif