staging: comedi: comedi_pci: dev->board_name is always valid

The dev->board_name is always initialized before calling the(*attach)
or (*auto_attach) function. It's no longer necessary to validate the
pointer in comedi_pci_enable().

Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Reviewed-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>