staging: dgap: Simplify and cleanup dgap_init_module function

This patch simplifies and cleans up the dgap_init_module function. It also fixes
a possible double free condition as a result pci_unregister_driver possibly
being called twice.

Signed-off-by: Mark Hounschell <markh@compro.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>