staging: unisys: use local variable in cleanup

the dev_t was being stored in visorchipset_platform_device.dev.devt
while initializing the module. so pass that value as an argument to
cleanup() so that it can use this local variable instead of the global
variable.

Signed-off-by: Sudip Mukherjee <sudip@vectorindia.org>
Reviewed-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Benjamin Romer <benjamin.romer@unisys.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>