Makefile.dtbo: Suppress time information for ufdt_apply_overlay

Every time ufdt_apply_overlay runs, a message about how long
ufdt_apply_overlay took is generated. This message is not interesting
for verifying whether the DTBO is applies correctly.

All error messages from ufdt_apply_overlay come on stderr, so re-route
stdout to /dev/null.

Change-Id: Iacd1ed0e08fde432fa886a03d3f48cee0bf8f416
Signed-off-by: Elliot Berman <[email protected]>

scripts/Makefile.dtbo

@@ -15,7 +15,7 @@ cmd_dtbo_verify = $(foreach m,\
 	$(addprefix $(obj)/,$($(@F)-base)),\
 		$(if $(m),\
 			$(DTC_OVERLAY_TEST) $(m) $@ \
-			$(dot-target).$(patsubst $(obj)/%.dtb,%,$(m)).tmp;))\
+			$(dot-target).$(patsubst $(obj)/%.dtb,%,$(m)).tmp > /dev/null;))\
 			true
 else
 cmd_dtbo_verify = true