gpio: stmpe: drop references to "virtual" IRQ, fix bug

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.

When doing this I see that the hwirq argument is used
for mapping rather than the Linux IRQ in the map function.
This doesn't look right. Use the Linux IRQ instead.

I cannot test this patch so I don't know if the mapping change
is correct, however since absolutely every other driver does
it the other way around this doesn't look sound at all. Please
help out with review.

Cc: Vipul Kumar Samar <vipulkumar.samar@st.com>
Cc: Lee Jones <lee.jones@linaro.org>
Cc: Gabriel Fernandez <gabriel.fernandez@st.com>
Cc: Jean-Nicolas Graux <jean-nicolas.graux@st.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>