BUG/MINOR: pattern: Add a missing HA_SPIN_INIT() in pat_ref_newid()

pat_ref_newid() is lacking a spinlock init. It was probably forgotten
in b5997f740b ("MAJOR: threads/map: Make acls/maps thread safe").

Signed-off-by: Aurélien Nephtali <aurelien.nephtali@corp.ovh.com>
diff --git a/src/pattern.c b/src/pattern.c
index fe672f1..2eb8265 100644
--- a/src/pattern.c
+++ b/src/pattern.c
@@ -1906,7 +1906,7 @@
 	ref->unique_id = unique_id;
 	LIST_INIT(&ref->head);
 	LIST_INIT(&ref->pat);
-
+	HA_SPIN_INIT(&ref->lock);
 	LIST_ADDQ(&pattern_reference, &ref->list);
 
 	return ref;