mtd: rawnand: cadence: reinit completion before executing a new command

Reing the completion object before executing CDMA command to make sure
the 'done' flag is OK.

Fixes: ec4ba01e ("mtd: rawnand: Add new Cadence NAND driver to MTD subsystem")
Cc: stable@vger.kernel.org
Signed-off-by: Piotr Sroka <piotrs@cadence.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/1581328530-29966-4-git-send-email-piotrs@cadence.com