wireless-regdb: set PKGARCH:=all

As it's an architecture-independent binary file.

Ref: https://github.com/openwrt/openwrt/pull/1521#issuecomment-514687053
Suggested-by: Deng Qingfang <dengqf6@mail2.sysu.edu.cn>
Signed-off-by: Petr Štetiar <ynezz@true.cz>
(cherry picked from commit 57d1c05ec9)

package/firmware/wireless-regdb/Makefile

@@ -12,6 +12,7 @@ PKG_MAINTAINER:=Felix Fietkau <nbd@nbd.name>
 include $(INCLUDE_DIR)/package.mk
 
 define Package/wireless-regdb
+	PKGARCH:=all
 	SECTION:=firmware
 	CATEGORY:=Firmware
 	URL:=https://git.kernel.org/pub/scm/linux/kernel/git/sforshee/wireless-regdb.git/