I2C: cadence: Don't initialize vars on every try

When a transaction fails and is retried, some variables don't need to be
re-assigned and can be moved out of the code which is looping.

Signed-off-by: Soren Brinkmann <soren.brinkmann@xilinx.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>