[media] rc: meson-ir: use readl_relaxed in the interrupt handler

We don't need the memory barriers here and an interrupt handler should
be as fast as possible. Therefore switch to readl_relaxed.

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Reviewed-by: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Sean Young <sean@mess.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>