The only usage of the kf_ops field in the rftype struct is to pass it as
argument to __kernfs_create_file(), which accepts a pointer to const.
Make it a pointer to const. This makes it possible to make
rdtgroup_kf_single_ops and kf_mondata_ops const, which allows the
compiler to put them in read-only memory.
Signed-off-by: Rikard Falkeborn <rikard.falkeborn@xxxxxxxxx>