scripts: mkmakefile: set umask before calling BR's makefile

Small optimization so we don't have another 'make' level (caused by the
umask fix) when running the generated makefile.

Signed-off-by: Guido Martínez <guido@vanguardiasur.com.ar>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

support/scripts/mkmakefile

@@ -35,7 +35,7 @@ MAKEFLAGS += --no-print-directory
 all	:= \$(filter-out Makefile,\$(MAKECMDGOALS))
 
 _all:
-	\$(MAKE) \$(MAKEARGS) \$(all)
+	umask 0022 && \$(MAKE) \$(MAKEARGS) \$(all)
 
 Makefile:;