irq_domain: Fix debug output to use "irq" instead of "virq"

irq_domain: Fix debug output to use "irq" instead of "virq"

Back when irq_domain was a powerpc-only thing, the term "virq", or
virtual irq, was used to differentiate irq numbers from hardware irq
numbers.  However, virqs are synonymous with Linux irq numbers, so
using a different term is confusing.  This patch changes the debug
output to use the header "irq" instead of "virq" for the irq number
output column.

Signed-off-by: Grant Likely <grant.likely@secretlab.ca>