s390/sclp: add const to bin_attribute structure

Declare bin_attribute structure as const as it is only passed as an
argument to the function sysfs_create_bin_file. This argument is of
type const, so declare the structure as const.

Cross compiled for s390 architecture.

Signed-off-by: Bhumika Goyal <bhumirks@gmail.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>