If the device is unplugged and CONFIG_IIO is not supported, this will
result in a warning message at kernel/workqueue.

Only cancel delayed work in mcp2221_remove(), when CONFIG_IIO is enabled.
Signed-off-by: Abdelrahman Morsy <abdelrahmanhesham94@gmail.com>
Signed-off-by: Jiri Kosina <jkosina@suse.com>