ata: ep93xx: cut drvdata assignment

ata_host_alloc_pinfo() assigns the host pointer to the
struct device * drvdata, do not assign drv_data like this.
Since ata_host_alloc_pinfo() is called after this site, the
correct value is set eventually, but this assignment is just
plain pointless.

Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Tejun Heo <tj@kernel.org>