media: hantro: use G1_REG_INTERRUPT directly for the mpeg2

Use the register directly over the existing SWREG().

Ideally we'll port the driver away from the local registers, but for
now this is enough. For context - I was reading through the IRQ register
handling across the variants.

Acked-by: Nicolas Ferre <nicolas.ferre@microchip.com>
Reviewed-by: Ezequiel Garcia <ezequiel@collabora.com>
Signed-off-by: Emil Velikov <emil.velikov@collabora.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>