x86/resctrl: Remove unused struct mbm_state::chunks_bw

Nothing reads struct mbm_states's chunks_bw value, its a copy of
chunks. Remove it.

Signed-off-by: James Morse <james.morse@arm.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Reinette Chatre <reinette.chatre@intel.com>
Link: https://lkml.kernel.org/r/20200708163929.2783-2-james.morse@arm.com