pnpacpi: fix potential corruption on "pnpacpi: exceeded the max number of IRQ resources 2"

PNP_MAX_IRQ is 2
If a device invokes pnpacpi_parse_allocated_irqresource() 0, 1, or 2 times, we are happy.
The 3rd time, we will fail and print "pnpacpi: exceeded the max number of IRQ resources: 2"
The 4th and subsequent calls (if this ever happened) would silently scribble on
irq_resource[2], which doesn't actualy exist.

Found-by: Bjorn Helgaas <bjorn.helgaas@hp.com>
Signed-off-by: Len Brown <len.brown@intel.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>