This fixes a bug introduced with:

commit 74c3632
Author: Antony Pavlov <antonynpavlov@gmail.com>
Date:   Tue Oct 18 13:48:44 2011 +0400

    fs: fix path_check_prereq()

    This patch makes impossible the situations than path_check_prereq() can make
    'return 0' without changing errno.

    Signed-off-by: Antony Pavlov <antonynpavlov@gmail.com>
    Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

path_check_prereq is supposed to return 0 when a file does
not exist and S_UB_DOES_NOT_EXIST is given. stat() changes
errno, so we have to set errno back to 0 before returning.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>