ARM: dts: meson8b: use the actual frequency for the GPU's 364MHz OPP

The clock setup on Meson8 cannot achieve a Mali frequency of exactly
182.15MHz. The vendor driver uses "FCLK_DIV7 / 1" for this frequency,
which translates to 2550MHz / 7 / 1 = 364285714Hz.
Update the GPU operating point to that specific frequency to not confuse
myself when comparing the frequency from the .dts with the actual clock
rate on the system.

Fixes: c3ea80b6 ("ARM: dts: meson8b: add the Mali-450 MP2 GPU")
Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>