sysfs.h: fix __BIN_ATTR_RW()

__BIN_ATTR_RW() wasn't passing in the _size field.  As it would break
the build if this macro was ever used, it's obvious no one had ever
tried to use it before.

Fix it so that it can be used.

Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>