Staging: hv: hv_mouse: fix build warning

The trans_id variable (u64) was being incorrectly cast to a unsigned
long * when it should have just been unsigned long.

Fun with pointers, what a fricken mess, we need some real type safety
for these types of fields somehow...

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