sysfs: fix attribute_group bin file path on removal

Cody Schafer already fixed binary file creation for attribute groups, see [1].
This patch makes the appropriate changes for binary file removal
of attribute groups.
[1]: http://lkml.org/lkml/2014/2/27/832



Signed-off-by: Robert ABEL <rabel@cit-ec.uni-bielefeld.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>