package/zstd: Install tools into /usr/bin, not /usr/local/bin

Install tools into /usr/bin, not /usr/local/bin, since /usr/local/bin
is not in PATH by deafault.

[Peter: set PREFIX to /usr to really install into /usr/bin]
Signed-off-by: Andrey Smirnov <andrew.smirnov@gmail.com>
Tested-by: Bernd Kuhls <bernd.kuhls@t-online.de>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/zstd/zstd.mk

@@ -43,7 +43,7 @@ endef
 
 define ZSTD_INSTALL_TARGET_CMDS
 	$(TARGET_MAKE_ENV) $(TARGET_CONFIGURE_OPTS) $(MAKE) $(ZSTD_OPTS) \
-		DESTDIR=$(TARGET_DIR) -C $(@D)/programs install
+		DESTDIR=$(TARGET_DIR) PREFIX=/usr -C $(@D)/programs install
 endef
 
 $(eval $(generic-package))