serial: remove unnecessary platform_set_drvdata()

serial: remove unnecessary platform_set_drvdata()

The driver core clears the driver data to NULL after device_release
or on probe failure, since commit bcb6fcf1119586a8b03889dfc51669b0ad6d4f95
(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 <jg1.han@samsung.com>
Acked-by: Barry Song <baohua.song@csr.com>
Acked-by: Tony Prisk <linux@prisktech.co.nz>
Acked-by: Shawn Guo <shawn.guo@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>