Staging: comedi: quatech_daqp_cs.c: fix up the irq

The irq needs to return the correct type.  Also fix up some other
sparse warnings that were found.

Cc: Ian Abbott <abbotti@mev.co.uk>
Cc: Frank Mori Hess <fmhess@users.sourceforge.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>