HID: hid-lg4ff: Protect concurrent access to output HID report

Protect concurrent access to output HID report with a spinlock. The HID report
structure used to submit commands to wheels is shared amongst all functions that
need to do so and some of these functions can be executed in parallel.
Additionally, lg4ff_play() can be called from interrupt context by ff-memless
module. Locking is necessary to prevent sending bogus data to the wheels.

Signed-off-by: Michal Malý <madcatxster@devoid-pointer.net>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>