mcp23s08: remove unused work queue

Never accessed anywhere.
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>

drivers/gpio/gpio-mcp23s08.c

@@ -4,7 +4,6 @@
 
 #include <linux/kernel.h>
 #include <linux/device.h>
-#include <linux/workqueue.h>
 #include <linux/mutex.h>
 #include <linux/gpio.h>
 #include <linux/spi/spi.h>
@@ -60,8 +59,6 @@ struct mcp23s08 {
 
 	struct gpio_chip	chip;
 
-	struct work_struct	work;
-
 	const struct mcp23s08_ops	*ops;
 };