mtd: nand: atmel_nand: remove unnecessary platform_set_drvdata()

mtd: nand: atmel_nand: remove unnecessary platform_set_drvdata()

The driver core clears the driver data to NULL after device_release
or on probe failure, since commit 0998d0631001288a5974afc0b2a5f568bcdecb4d
(device-core: Ensure drvdata = NULL when no driver is bound).
Thus, it is not needed to manually clear the device driver data to NULL.

Signed-off-by: Jingoo Han <[email protected]>
Acked-by: Josh Wu <[email protected]>
Signed-off-by: Artem Bityutskiy <[email protected]>
Signed-off-by: David Woodhouse <[email protected]>