staging: comedi: me4000: refactor request_irq() during attach

Do the request_irq() before setting up the subdevices. This removes an
indent level and makes the code a bit cleaner.

Also, remove the dev_warn() noise about the irq.

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>