uboot-imx

sf: Get spi locally from spi_flash

For better code readabilty, get the spi pointer from
spi_flash{} locally and use it instead of direct
dereferring spi pinter as flash->spi->*

Tested-by: Jagan Teki <jteki@openedev.com>
Tested-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Signed-off-by: Jagan Teki <jteki@openedev.com>