sf: Fix look for the fastest read command

Few of the spi controllers are only supports array slow
read which is quite different behaviour compared to others.

So this fix on sf will correctly handle the slow read supported
controllers.

Signed-off-by: Jagannadha Sutradharudu Teki <jagannadh.teki@gmail.com>
Tested-by: Bin Meng <bmeng.cn@gmail.com>
3 files changed