staging: gpib: fix unset padding field copy back to userspace

In the Linux kernel, the following vulnerability has been resolved:

staging: gpib: fix unset padding field copy back to userspace

The introduction of a padding field in the gpib_board_info_ioctl is showing up as initialized data on the stack frame being copyied back to userspace in function board_info_ioctl. The simplest fix is to initialize the entire struct to zero to ensure all unassigned padding fields are zero'd before being copied back to userspace.