package/openswan: fix parallel build

Fixes:
    http://autobuild.buildroot.org/results/2ec/2ecb098b01bd44d75182b15f98c1fd2a8c927438/
    http://autobuild.buildroot.org/results/18f/18f0166f3fa831f321818e286d9c2e9037f8c8d0/
    ...

Cc: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/openswan/openswan.mk

@@ -29,12 +29,12 @@ endif
 endif
 
 define OPENSWAN_BUILD_CMDS
-	$(TARGET_MAKE_ENV) $(MAKE) -C $(@D) \
+	$(TARGET_MAKE_ENV) $(MAKE1) -C $(@D) \
 		$(OPENSWAN_MAKE_OPTS) programs
 endef
 
 define OPENSWAN_INSTALL_TARGET_CMDS
-	$(TARGET_MAKE_ENV) $(MAKE) -C $(@D) \
+	$(TARGET_MAKE_ENV) $(MAKE1) -C $(@D) \
 		$(OPENSWAN_MAKE_OPTS) DESTDIR=$(TARGET_DIR) install
 endef