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: Haojian Zhuang <haojian.zhuang@linaro.org>
Cc: Rob Herring <rob.herring@calxeda.com>
Acked-by: NBaruch Siach <baruch@tkos.co.il>
Signed-off-by: NLinus Walleij <linus.walleij@linaro.org>