dp: swdp_bitbang: fix unused variable build error

The variable config in sw_port_off() is not used, and it's
causing CI build error about unused variable. So remove it.

(cherry picked from commit 1ec5ce0)

Original-Signed-off-by: Daniel Leung <daniel.leung@intel.com>
GitOrigin-RevId: 1ec5ce0
Cr-Build-Id: 8734199375406094193
Cr-Build-Url: https://cr-buildbucket.appspot.com/build/8734199375406094193
Copybot-Job-Name: zephyr-main-copybot-downstream
Change-Id: I1f055cb8d11f0a9d78fbe88f4cee88ccb1a86ca8
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/zephyr/+/5927200
Reviewed-by: Jeremy Bettis <jbettis@chromium.org>
Commit-Queue: Jeremy Bettis <jbettis@chromium.org>
Tested-by: ChromeOS Prod (Robot) <chromeos-ci-prod@chromeos-bot.iam.gserviceaccount.com>
Tested-by: Jeremy Bettis <jbettis@chromium.org>

drivers/dp/swdp_bitbang.c

@@ -677,7 +677,6 @@ static int sw_port_off(const struct device *dev)
 
 static int sw_gpio_init(const struct device *dev)
 {
-	const struct sw_config *config = dev->config;
 	struct sw_cfg_data *sw_data = dev->data;
 	int ret;