Rename the argument "virq" to just "irq", this IRQ isn't any
more "virtual" than any other Linux IRQ number, we use "hwirq"
for the actual hw-numbers, "virq" is just bogus.

Cc: Magnus Damm <damm@opensource.se>
Reviewed-by: Ian Molton <ian.molton@codethink.co.uk>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>