staging: comedi: acl7225b: remove local var in acl7225b_attach()

The 'iorange' local variable is only used in the request_region()
call. Remove the variable and just use the board->io_range directly.

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