Input: vmmouse - fix absolute device registration

We should set device's capabilities first, and then register it,
otherwise various handlers already present in the kernel will not be
able to connect to the device.

Reported-by: Lauri Kasanen <cand@gmx.com>
Cc: stable@vger.kernel.org
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>