raw/cnxk_gpio: check pointer before use in self test

Even though nonexistent cnxk_gpio is unlikely at this point
it's a good practice to check pointers before using them.

Fixes: 0e6557b448 ("raw/cnxk_gpio: add self test")
Coverity issue: 376502

Signed-off-by: Tomasz Duszynski <tduszynski@marvell.com>
Reviewed-by: Jerin Jacob <jerinj@marvell.com>

drivers/raw/cnxk_gpio/cnxk_gpio_selftest.c

@@ -311,6 +311,8 @@ cnxk_gpio_selftest(uint16_t dev_id)
 	int ret, ret2;
 
 	rawdev = rte_rawdev_pmd_get_named_dev("cnxk_gpio");
+	if (!rawdev)
+		return -ENODEV;
 	gpiochip = rawdev->dev_private;
 
 	queues = rte_rawdev_queue_count(dev_id);