Use si_drv1 to hold the softc for the adb_mouse character device instead of using devclass_get_softc().
Use si_drv1 to hold the softc for the adb_mouse character device instead of
using devclass_get_softc().

Tested by:	nwhitehorn

jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase,jrobhoward/SCADAbase