staging: vchiq_arm: Make vchiq_shutdown never fail

Most of the users of vchiq_shutdown ignore the return value,
which is bad because this could lead to resource leaks.
So instead of changing all calls to vchiq_shutdown, it's easier
to make vchiq_shutdown never fail.

Fixes: 71bad7f08641 ("staging: add bcm2708 vchiq driver")
Signed-off-by: Stefan Wahren <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/staging/vc04_services/interface/vchiq_arm/vchiq_arm.c

···
 	struct vchiq_state *state = instance->state;
 	int ret = 0;
 
-	if (mutex_lock_killable(&state->mutex))
-		return -EAGAIN;
+	mutex_lock(&state->mutex);
 
 	/* Remove all services */
 	vchiq_shutdown_internal(state, instance);