i3c: master: svc: Flush FIFO before sending Dynamic Address Assignment(DAA)

Ensure the FIFO is empty before issuing the DAA command to prevent
incorrect command data from being sent. Align with other data transfers,
such as svc_i3c_master_start_xfer_locked(), which flushes the FIFO before
sending a command.

Signed-off-by: Frank Li <Frank.Li@nxp.com>
Reviewed-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/r/20250129162250.3629189-1-Frank.Li@nxp.com


Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>