i2c: sprd: Fix the i2c count issue

We found the I2C controller count register is unreliable sometimes,
that will cause I2C to lose data. Thus we can read the data count
from 'i2c_dev->count' instead of the I2C controller count register.

Signed-off-by: Baolin Wang <baolin.wang@linaro.org>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>