i2c: i2c-cdns: Fix write transaction state

Start write transfer after loading data to FIFO.

Signed-off-by: Sai Pavan Boddu <sai.pavan.boddu@xilinx.com>
Reviewed-by: Ashok Reddy Soma <ashok.reddy.soma@xilinx.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>
Link: https://lore.kernel.org/r/f0b3e443daa7758e00dfdcc245cf6b2120b0e907.1646122610.git.michal.simek@xilinx.com