block: xsysace: Don't use NO_IRQ

Drivers shouldn't use NO_IRQ. Microblaze and PPC
define NO_IRQ as 0 and this reference will be removed
in near future.

Signed-off-by: Michal Simek <monstr@monstr.eu>
Reviewed-by: Ryan Mallon <rmallon@gmail.com>
Acked-by: Grant Likely <grant.likely@secretlab.ca>
CC: Rob Herring <rob.herring@calxeda.com>