kernel/gpio-button-hotplug: drop Build/Prepare rule in favor of default one

Signed-off-by: Alexandru Ardelean <ardeleanalex@gmail.com>

package/kernel/gpio-button-hotplug/Makefile

@@ -36,11 +36,6 @@ MAKE_OPTS:= \
 	CROSS_COMPILE="$(TARGET_CROSS)" \
 	SUBDIRS="$(PKG_BUILD_DIR)"
 
-define Build/Prepare
-	mkdir -p $(PKG_BUILD_DIR)
-	$(CP) ./src/* $(PKG_BUILD_DIR)/
-endef
-
 define Build/Compile
 	$(MAKE) -C "$(LINUX_DIR)" \
 		$(MAKE_OPTS) \