staging: gpib: Fix device reference leak in fmh_gpib driver

The fmh_gpib driver contains a device reference count leak in
fmh_gpib_attach_impl() where driver_find_device() increases the
reference count of the device by get_device() when matching but this
reference is not properly decreased. Add put_device() in
fmh_gpib_detach(), which ensures that the reference count of the
device is correctly managed.

Found by code review.

Cc: stable <[e-mail]>
Fixes: 8e4841a0888c ("staging: gpib: Add Frank Mori Hess FPGA PCI GPIB driver")
Signed-off-by: Ma Ke <[e-mail]>
Reviewed-by: Dan Carpenter <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/staging/gpib/fmh_gpib/fmh_gpib.c

···
 					   resource_size(e_priv->gpib_iomem_res));
 	}
 	fmh_gpib_generic_detach(board);
+
+	if (board->dev) {
+		put_device(board->dev);
+		board->dev = NULL;
+	}
 }
 
 static int fmh_gpib_pci_attach_impl(struct gpib_board *board,