HID: roccat: free buffered reports when destroying device

roccat_report_event() duplicates each report with kmemdup() and stores
the allocation in a circular-buffer slot. The allocation is released only
when that slot is reused.

The device destruction paths free struct roccat_device without releasing
reports still stored in cbuf[]. This makes those allocations unreachable
and leaks up to ROCCAT_CBUF_SIZE report buffers per device.

Add a small destructor that frees every buffered report before freeing the
device, and use it in both paths that can destroy a registered device.

Fixes: 206f5f2fcb5f ("HID: roccat: propagate special events of roccat hardware to userspace")
Cc: stable@vger.kernel.org
Signed-off-by: Xu Rao <raoxu@uniontech.com>
Signed-off-by: Jiri Kosina <jkosina@suse.com>