spi: sunxi: drop max_hz handling

spi: sunxi: drop max_hz handling

The driver is trying to read the "spi-max-frequency" property of the
*controller* driver node. There is no such property. The
"spi-max-frequency" property belongs to the SPI devices on the bus.

Right now, the driver will always fall back to the default value of 1MHz
and thus flash reads are very slow with just about 215kb/s.

In fact, the SPI uclass will already take care of everything and we just
have to clamp the frequency to the values the driver/hardware supports.
Thus, drop the whole max_hz handling.

Signed-off-by: Michael Walle <mwalle@kernel.org>
Reviewed-by: Andre Przywara <andre.przywara@arm.com>
Tested-by: Andre Przywara <andre.przywara@arm.com>