Makefile.config: don't silent twice

Here $(Q) is substituted with either @ or nothing, depending on
whether V is set, to either have verbose output or not. So, it does
not make sense to add another @.

Reviewed-by: Cyrill Gorcunov <gorcunov@gmail.com>
Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>
Signed-off-by: Andrei Vagin <avagin@gmail.com>