evdev: Release eventual input device grabs when getting disconnected

When getting disconnected we need to release eventual grabs on the
underlying input device as we also release the input device itself.
Otherwise, we would try to release the grab when the client that
requested it closes its handle, accessing the input device which
might already be freed.

Signed-off-by: Björn Steinbrink <B.Steinbrink@gmx.de>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>