drivers: gpio: infineon: remove redundant NULL check in ISR

Remove a redundant NULL check on the device pointer in the GPIO
interrupt handler.

The device pointer is dereferenced unconditionally before the check
and cannot be NULL in this context.

No functional change intended.

Signed-off-by: Gaetan Perrot <gaetan.perrot@spacecubics.com>

drivers/gpio/gpio_infineon.c

@@ -172,10 +172,7 @@ static void gpio_isr_handler(const struct device *dev)
 		Cy_GPIO_ClearInterrupt(base, i);
 	}
 
-	if (dev) {
-		gpio_fire_callbacks(&((struct gpio_cat1_data *const)(dev)->data)->callbacks, dev,
-				    pins);
-	}
+	gpio_fire_callbacks(&((struct gpio_cat1_data *const)(dev)->data)->callbacks, dev, pins);
 }
 #endif