mmc: meson-gx: use per port interrupt names

mmc: meson-gx: use per port interrupt names

So far the driver name is used as interrupt description, therefore in
/proc/interrupts it's not possible to tell which interrupt belongs to
which port. Change this by switching to NULL what causes the default
(device name) to be used. In our case that's the DT node name.

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Reviewed-by: Kevin Hilman <khilman@baylibre.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>