staging: dgap: new arguments to dgap_stop

In a later patch we will remove the duplicate codes. But the code also
needs to execute dgap_remove_driver_sysfiles() if it is being called
from dgap_remove_one() but if being called fron the error path of the
dgap_init_module() then the sysfiles should not be removed.

Signed-off-by: Sudip Mukherjee <sudip@vectorindia.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>