spi clock frequency problem on sunxi a20

[sayyed mohsen Zahraee]

i use spidev for receiving data from spi0

for low speed it works

./spidev_fdx /dev/spidev0.0 -r 16
/dev/spidev0.0: spi mode 0x0, 8 bits per word, 50000 Hz max
read(16, 16): 01 56, 0c 24 b8 06 70 03 b0 b6 ff 66 03 b0 c4 ff

but for higher speed i get nothings and all data is zero

./spidev_fdx /dev/spidev0.0 -r 16
/dev/spidev0.0: spi mode 0x0, 8 bits per word, 1000000 Hz max

read(16, 16): 06 00, 00 00 00 00 00 00 00 00 00 00 00 00 00 00

it works up to 100000 HZ  and above values will fail

i test my spi with IMX6 and it works but on my cubieboard2 it works only for lower speeds