HID: hyperv: Properly disconnect the input device

When we unload the mouse driver, properly disconnect the input device.

Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
Signed-off-by: Haiyang Zhang <haiyangz@microsoft.com>
Reported-by: Fuzhou Chen <fuzhouch@microsoft.com>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>