i2c: xilinx: Removed unnecessary set tx direction in write operation

The driver is following the Dynamic controller logic flow.
As per Dynamic controller logic flow this bit need not to be set.

Signed-off-by: Kedareswara rao Appana <appanad@xilinx.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>