powerpc/83xx/mpc8349emitx: Drop unused variable

Commit 5d354dc3 ("powerpc/83xx/mpc8349emitx: Make
mcu_gpiochip_remove() return void") removed the usage of the variable
ret, but failed to remove the variable itself, resulting in:

	arch/powerpc/platforms/83xx/mcu_mpc8349emitx.c: In function ‘mcu_remove’:
	arch/powerpc/platforms/83xx/mcu_mpc8349emitx.c:189:6: error: unused variable ‘ret’ [-Werror=unused-variable]
	  189 |  int ret;
	      |      ^~~

So remove the variable now.
Reported-by: Linux Kernel Functional Testing <lkft@linaro.org>
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20211110110739.1072634-1-u.kleine-koenig@pengutronix.de

arch/powerpc/platforms/83xx/mcu_mpc8349emitx.c

@@ -186,7 +186,6 @@ static int mcu_probe(struct i2c_client *client)
 static int mcu_remove(struct i2c_client *client)
 {
 	struct mcu *mcu = i2c_get_clientdata(client);
-	int ret;
 
 	kthread_stop(shutdown_thread);