tree-wide: move logging from varlink clients in nsresource.c/dissect-image.c into callers

These calls are "library-like", hence better should only debug log on
their own, not more.

src/dissect/dissect.c

@@ -2261,7 +2261,7 @@ static int run(int argc, char *argv[]) {
                                         arg_flags,
                                         &m);
                         if (r < 0)
-                                return r;
+                                return log_error_errno(r, "Failed to mount image via mountfsd: %m");
                 }
         }