While updating how mmap enabled kernfs files are handled by lockdep,
9b2db6e1 ("sysfs: bail early from kernfs_file_mmap() to avoid
spurious lockdep warning") inadvertently dropped error return check
from kernfs_file_mmap().  The intention was just dropping "if
(ops->mmap)" check as the control won't reach the point if the mmap
callback isn't implemented, but I mistakenly removed the error return
check together with it.

This led to Xorg crash on i810 which was reported and bisected to the
commit and then to the specific change by Tobias.
Signed-off-by: NTejun Heo <tj@kernel.org>
Reported-and-bisected-by: NTobias Powalowski <tobias.powalowski@googlemail.com>
Tested-by: NTobias Powalowski <tobias.powalowski@googlemail.com>
References: http://lkml.kernel.org/g/533D01BD.1010200@googlemail.com
Cc: stable <stable@vger.kernel.org> # 3.14
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>