x86/MCE-telem: drop unnecessary per-CPU field

struct mc_telem_cpu_ctl's processing field is used solely in
mctelem_process_deferred(), where the local variable can as well be used
directly when retrieving the head of the list to process. This then also
eliminates the field holding a dangling pointer once the processing of
the list finished, in particular when the entry is handed to
mctelem_dismiss().

No functional change intended.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>

xen/arch/x86/cpu/mcheck/mctelem.c

@@ -122,7 +122,6 @@ struct mc_telem_cpu_ctl {
 	 * to guarantee the above mutual exclusivity.
 	 */
 	struct mctelem_ent *pending, *lmce_pending;
-	struct mctelem_ent *processing;
 };
 static DEFINE_PER_CPU(struct mc_telem_cpu_ctl, mctctl);
 
@@ -233,9 +232,7 @@ void mctelem_process_deferred(unsigned int cpu,
 	 * handled by another round of MCE softirq.
 	 */
 	mctelem_xchg_head(lmce ? &ctl->lmce_pending : &ctl->pending,
-			  &this_cpu(mctctl.processing), NULL);
-
-	head = this_cpu(mctctl.processing);
+			  &head, NULL);
 
 	/*
 	 * Then, fix up the list to include prev pointers, to make