Driver core clears the driver data to NULL after device_release or on
probe failure, so just remove it from here.

The relevant driver core change was commit 0998d063 ("device-core:
Ensure drvdata = NULL when no driver is bound").
Signed-off-by: Michal Simek <michal.simek@xilinx.com>
Cc: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>