staging: comedi: s626: cleanup request_irq in s626_attach_pci()

Only set dev->irq if request_irq is successfull.

Remove the kernel message noise.

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>