HID: Remove the semaphore driver_lock

The semaphore 'driver_lock' is used as a simple mutex, and also unnecessary as
suggested by Arnd. Hence removing it, as the concurrency between the probe and
remove is already handled in the driver core.

Suggested-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Binoy Jayan <binoy.jayan@linaro.org>
Acked-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>
Reviewed-by: David Herrmann <dh.herrmann@gmail.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>