Use via_isa_set_irq() which better encapsulates irq handling in the
vt82xx model and avoids using isa_get_irq() that has a comment saying
it should not be used.

Signed-off-by: BALATON Zoltan <balaton@eik.bme.hu>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-Id: <26cb1848c9fc0360df7a57c2c9ba5e03c4a692b5.1634259980.git.balaton@eik.bme.hu>
Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>