staging: gpib: Enable SRQ irq on request_system_control

staging: gpib: Enable SRQ irq on request_system_control

The SRQ irq was being enabled on attach but the board is not
set up to handle it until it becomes system controller.

Move the enabling of the SRQ irq to bb_request_system_control.

Fixes: 4cd654f84769 ("staging: gpib: Add gpio bitbang GPIB driver")
Tested-by: Dave Penkler <dpenkler@gmail.com>
Signed-off-by: Dave Penkler <dpenkler@gmail.com>
Link: https://lore.kernel.org/r/20250418173434.2892-4-dpenkler@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>