build: Silence dtc directory creation

Align with other mkdir calls.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-Id: <0dd4c8f5-d60e-e564-652f-cd0101f6ee68@web.de>
Message-Id: <20180415230522.24404-5-f4bug@amsat.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

Makefile

@@ -485,7 +485,7 @@ subdir-dtc: .git-submodule-status dtc/libfdt dtc/tests
 	$(call quiet-command,$(MAKE) $(DTC_MAKE_ARGS) CPPFLAGS="$(DTC_CPPFLAGS)" CFLAGS="$(DTC_CFLAGS)" LDFLAGS="$(LDFLAGS)" ARFLAGS="$(ARFLAGS)" CC="$(CC)" AR="$(AR)" LD="$(LD)" $(SUBDIR_MAKEFLAGS) libfdt/libfdt.a,)
 
 dtc/%: .git-submodule-status
-	mkdir -p $@
+	@mkdir -p $@
 
 # Overriding CFLAGS causes us to lose defines added in the sub-makefile.
 # Not overriding CFLAGS leads to mis-matches between compilation modes.