Staging: Gasket: fix a couple off by one bugs

The > should be >= or we end up writing one element beyond the end of
the interrupt_data->eventfd_ctxs[] array.

Fixes: 9a69f508 ("drivers/staging: Gasket driver framework + Apex driver")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>