arm64: dts: meson-g12a-sei510: bump bluetooth bus speed to 2Mbaud/s

Setting to 2Mbaud/s is the nominal bus speed for common usages.

Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Acked-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>