md/raid5: remove unused working_disks variable

clang with W=1 reports
drivers/md/raid5.c:7719:6: error: variable 'working_disks'
  set but not used [-Werror,-Wunused-but-set-variable]
        int working_disks = 0;
            ^
This variable is not used so remove it.
Signed-off-by: Tom Rix <trix@redhat.com>
Signed-off-by: Song Liu <song@kernel.org>
Link: https://lore.kernel.org/r/20230327132324.1769595-1-trix@redhat.com

drivers/md/raid5.c

@@ -7716,7 +7716,6 @@ static void raid5_set_io_opt(struct r5conf *conf)
 static int raid5_run(struct mddev *mddev)
 {
 	struct r5conf *conf;
-	int working_disks = 0;
 	int dirty_parity_disks = 0;
 	struct md_rdev *rdev;
 	struct md_rdev *journal_dev = NULL;
@@ -7912,10 +7911,8 @@ static int raid5_run(struct mddev *mddev)
 			pr_warn("md: cannot handle concurrent replacement and reshape.\n");
 			goto abort;
 		}
-		if (test_bit(In_sync, &rdev->flags)) {
-			working_disks++;
+		if (test_bit(In_sync, &rdev->flags))
 			continue;
-		}
 		/* This disc is not fully in-sync.  However if it
 		 * just stored parity (beyond the recovery_offset),
 		 * when we don't need to be concerned about the