Staging: hv: mousevsc: Get rid of the struct input_device_context

The state maintained in struct input_device_context can easily be included
in the struct mousevsc_dev structure. Simplify the code by consolidating
the state.

Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
Signed-off-by: Haiyang Zhang <haiyangz@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>