drivers/w1/masters/mxc_w1.c: remove unnecessary platform_set_drvdata()

The driver core clears the driver data to NULL after device_release or on
probe failure.  Thus, it is not needed to manually clear the device driver
data to NULL.

Signed-off-by: Jingoo Han <jg1.han@samsung.com>
Cc: Evgeniy Polyakov <zbr@ioremap.net>
Cc: Greg KH <greg@kroah.com>
Acked-by: Shawn Guo <shawn.guo@linaro.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>