staging: unisys: use local variable

we are getting dev_t as an argument in the function, so use the local
variable instead of the global variable "majordev".
this global variable will be removed in one of the next patch of the
series.

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>