staging: comedi: ni_daq_700: remove local variable in the 'attach' function

There is no need for the local variable 'iobase' in the attach
function. If it's '0' the attach fails otherwise the value is
just stored in dev->iobase.

Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Cc: Ian Abbott <abbotti@mev.co.uk>
Cc: Frank Mori Hess <fmhess@users.sourceforge.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>