Drivers: w1: remove last __devexit_p() instance

This slipped in through the merging of different trees.  Remove
__devexit_p() use in the mxc_w1 driver.

Cc: Evgeniy Polyakov <zbr@ioremap.net>
Cc: Fabio Estevam <fabio.estevam@freescale.com>
Cc: Bill Pemberton <wfp5p@virginia.edu>
Cc: Sascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>